Can someone please help me! Does anyone have a list of decorations that..

Here are all the possible items to get in Ruby, and their locations.

Desks:

Brick Desk: Fortree City Shop.
Camp Desk: Fortree City Shop.
Comfort Desk: Fortree City Shop.
Hard Desk: Fortree City Shop.
Heavy Desk: Fortree City Shop.
Pretty Desk: Route 113 Glass Workshop (after getting 8,000 steps worth of ash in your Soot Sack, then giving it ot the Glass Maker).
Pokemon Desk: Fortree City Shop.
Ragged Desk: Fortree City Shop.
Small Desk: Fortree City Shop.

Chairs:

Brick Chair: Fortree City Shop.
Camp Chair: Fortree City Shop.
Comfort Chair: Fortree City Shop.
Hard Chair: Fortree City Shop.
Heavy Chair: Fortree City Shop.
Pretty Chair: Route 113 Glass Workshop (after collecting 6,000 steps worth of ash in your Soot Sack and giving it to the Glass Maker).
Pokemon Chair: Fortree City Shop.
Ragged Chair: Fortree City Shop.
Small Chair: Fortree City Shop.

Plants:

Big Plant: Route 104 Shop.
Colorful Plant: Route 104 Shop.
Gorgeous Plant: Route 104 Shop.
Pretty Flower: Route 104 Shop.
Red Plant: Route 104 Shop.
Tropical Plant: Route 104 Shop.

Ornaments:

Blue Balloon: Top left store of Slateport City Market (after you have received TM 43 Secret Power).
Blue Brick: Top left store of Slateport City Market (after you have received TM 43 Secret Power).
Blue Tent: Received from Trick Master after completing 8th Trick House Challenge (Sapphire Version only).
Breakable Door: Rooftop of Lilycove Department Store (Clearout Sale only, occurs after defeating Elite Four and Steven).
Cute TV: Rooftop of Lilycove Department Store (Clearout Sale only, occurs after defeating Elite Four and Steven).
Fence Length: Rooftop of Lilycove Department Store (Clearout Sale only, occurs after defeating Elite Four and Steven).
Fence Width: Rooftop of Lilycove Department Store (Clearout Sale only, occurs after defeating Elite Four and Steven).
Glass Ornament: Lilycove Museum Curator (after having 5 of your Pokemon put on display on Second Floor of Museum).
Gold Shield: Battle Tower (after winning 100 battles in a row).
Mud Ball: Rooftop of Lilycove Department Store (Clearout Sale only, occurs after defeating Elite Four and Steven).
Red Balloon: Top left store of Slateport City Market (after you have received TM 43 Secret Power).
Red Brick: Top left store of Slateport City Market (after you have received TM 43 Secret Power).
Red Tent: Received from Trick Master after completing 8th Trick House Challenge (Ruby Version only).
Round TV: Rooftop of Lilycove Department Store (Clearout Sale only, occurs after defeating Elite Four and Steven).
Sand Ornament: Rooftop of Lilycove Department Store (Clearout Sale only, occurs after defeating Elite Four and Steven).
Silver Shield: Battle Tower (after winning 50 battles in a row).
Slide: Rooftop of Lilycove Department Store (Clearout Sale only, occurs after defeating Elite Four and Steven).
Solid Board: Rooftop of Lilycove Department Store (Clearout Sale only, occurs after defeating Elite Four and Steven).
Stand: Rooftop of Lilycove Department Store (Clearout Sale only, occurs after defeating Elite Four and Steven).
Tire: Rooftop of Lilycove Department Store (Clearout Sale only, occurs after defeating Elite Four and Steven).
TV: Rooftop of Lilycove Department Store (Clearout Sale only, occurs after defeating Elite Four and Steven).
Yellow Balloon: Top left store of Slateport City Market (after you have received TM 43 Secret Power).
Yellow Brick: Top left store of Slateport City Market (after you have received TM 43 Secret Power).

Mats:

Attract Mat: Far Right Counter, Fifth Floor, Lilycove Department Store.
B Note Mat: Top left store of Slateport City Market (after you have received TM 43 Secret Power).
C High Note Mat: Top left store of Slateport City Market (after you have received TM 43 Secret Power).
C Low Note Mat: Top left store of Slateport City Market (after you have received TM 43 Secret Power).
D Note Mat: Top left store of Slateport City Market (after you have received TM 43 Secret Power).
E Note Mat: Top left store of Slateport City Market (after you have received TM 43 Secret Power).
Fire Blast Mat: Far Right Counter, Fifth Floor, Lilycove Department Store.
Fissure Mat: Far Right Counter, Fifth Floor, Lilycove Department Store.
F Note Mat: Top left store of Slateport City Market (after you have received TM 43 Secret Power).
Glitter Mat: Far Right Counter, Fifth Floor, Lilycove Department Store.
G Note Mat: Top left store of Slateport City Market (after you have received TM 43 Secret Power).
Jump Mat: Far Right Counter, Fifth Floor, Lilycove Department Store.
Powder Snow Mat: Far Right Counter, Fifth Floor, Lilycove Department Store.
Spikes Mat: Far Right Counter, Fifth Floor, Lilycove Department Store.
Spin Mat: Far Right Counter, Fifth Floor, Lilycove Department Store.
Surf Mat: Far Right Counter, Fifth Floor, Lilycove Department Store.
Thunder Mat: Far Right Counter, Fifth Floor, Lilycove Department Store.

Posters:

Ball Poster: Far Right Counter, Fifth Floor, Lilycove Department Store.
Blue Poster: Far Right Counter, Fifth Floor, Lilycove Department Store.
Cute Poster: Far Right Counter, Fifth Floor, Lilycove Department Store.
Green Poster: Far Right Counter, Fifth Floor, Lilycove Department Store.
Kiss Poster: Unknown Pokemon Game (yet to be released).
Long Poster: Far Right Counter, Fifth Floor, Lilycove Department Store.
Pika Poster: Far Right Counter, Fifth Floor, Lilycove Department Store.
Red Poster: Far Right Counter, Fifth Floor, Lilycove Department Store.
Sea Poster: Far Right Counter, Fifth Floor, Lilycove Department Store.
Sky Poster: Far Right Counter, Fifth Floor, Lilycove Department Store.

Dolls:

Azurill Doll: Far Left Counter, Fifth Floor, Lilycove Department Store/Top left store of Slateport City Market (after you have received TM 43 Secret Power).
Baltoy Doll: Far Left Counter, Fifth Floor, Lilycove Department Store
Blastoise Doll: Unknown Pokemon Game (yet to be released).
Charizard Doll: Unknown Pokemon Game (yet to be released).
Chikorita Doll: Unknown Pokemon Game (yet to be released).
Clefairy Doll: Unknown Pokemon Game (yet to be released).
Cyndaquil Doll: Unknown Pokemon Game (yet to be released).
Ditto Doll: Unknown Pokemon Game (yet to be released).
Duskull Doll: Far Left Counter, Fifth Floor, Lilycove Department Store.
Gulpin Doll : Far Left Counter, Fifth Floor, Lilycove Department Store.
Jigglypuff Doll: Far Left Counter, Fifth Floor, Lilycove Department Store.
Kecleon Doll: Far Left Counter, Fifth Floor, Lilycove Department Store.
Lapras Doll: Unknown Pokemon Game (yet to be released).
Lotad Doll: Lanette's House, Route 114 (Sapphire Version only).
Marill Doll: Far Left Counter, Fifth Floor, Lilycove Department Store/Top left store of Slateport City Market (after you have received TM 43 Secret Power).
Meowth Doll: Unknown Pokemon Game (yet to be released).
Mudkip Doll: Mauville Game Corner.
Pichu Doll: Far Left Counter, Fifth Floor, Lilycove Department Store.
Pikachu Doll: Far Left Counter, Fifth Floor, Lilycove Department Store.
Regice Doll: Unknown Pokemon Game (yet to be released).
Regirock Doll: Unknown Pokemon Game (yet to be released).
Registeel Doll: Unknown Pokemon Game (yet to be released).
Rhydon Doll: Rooftop of Lilycove Department Store (Clearout Sale only, occurs only after you have defeated Elite Four and Steven).
Seedot Doll: Lanette's House, Route 114 (Ruby Version only).
Skitty Doll: Far Left Counter, Fifth Floor, Lilycove Department Store/Top left store of Slateport City Market (after you have received TM 43 Secret Power).
Smoochum Doll: Unknown Pokemon Game (yet to be released).
Snorlax Doll: Unknown Pokemon Game (yet to be released).
Swablu Doll: Far Left Counter, Fifth Floor, Lilycove Department Store.
Togepi Doll: Unknown Pokemon Game (yet to be released).
Torchic Doll: Mauville Game Corner.
Totodile Doll: Unknown Pokemon Game (yet to be released).
Treecko Doll: Mauville Game Corner.
Venusaur Doll: Unknown Pokemon Game (yet to be released).
Wailmer Doll Sootopolis City - Woman in house right of pokemon center/Rooftop of Lilycove Department Store (Clearout Sale only, occurs only after you have defeated Elite Four and Steven).
Wynaut Doll: Far Left Counter, Fifth Floor, Lilycove Department Store.

Hope this helps, because it took me a long time to write.

See ya!