Hi I have some questions. 1. I need to know which are the Diamond only..

1. Diamond
Seel, Dewgong, Scyther, Murkrow, Scizor, Larvitar, Pupitar, Tyranitar, Poochyena, Migthyena, Aron, Lairon, Aggron, Kecleon, Cranidos, Rampardos, Honchkrow, Stunky, Skuntank, Dialga
Pearl
Slowpoke, Slowbro, Pinsir, Slowking, Misdreavus, Houndour, Houndoom, Stantler, Spheal, Sealeo, Walrein, Bagon, Shelgon, Salamence, Sheildon, Bastiodon, Mismagius, Glameow, Purugly, Palkia

2. Togetic and Roselia use the Shiny Stone. Murkrow and Misdreavus use the Dusk Stone. Male Kirlia and Female Snorunt use the Dawn Stone

3. They are part of the National Dex because thier pre-evos aren't a part of the Sinnoh Dex so they can't be in. To get most of them, use one of the new stones on their pre-evos, have a certain move in thier moveset, or be holding an item and traded, or leveled up in a certain area

Well, there's only Stunkie in Diamond, and that's about it as far as I know.

1. Diamond only pokes: Dialga,Cranidos,Rampardos,Stunky,Skuntank,Murkrow,Honchkrow,Kecleon,Aron,Lairon,Aggron,Poochyena,Mightyena,Larvitar,Pupitar,Tyranitar,Scyther,Scizor,Seel,and Dewgong.

Pearl only pokes: Palkia,Slowpoke,Slowbro,Slowking,Pinsir,Houndour,Houndoom,Misdreavus,Mismagius, Bagon,Shelgon,Salamence,Sheildon,Bastiodon,Spheal,Sealeo,Walrien,Glameow, Purugly,and Stantler.


2. Happiny with the Oval Stone at Day or Morning evovles into Chansey.
Sneasle with the Razor Claw at nighttime evovles into Weavile.
Gligor at nighttime with the Razor Fang evovles into Gliscor.
Togetic with the Shiny Stone evovles into Togekiss.
Roselia with the Shiny Stone evovles into Roserade.
Murkrow with the Dusk Stone evovles into Honchkrow.
Misdreeavus with the Dusk Stone evovles into Mismagius.
Male Kirlia with the Dawn Stone evovles into Gallade.
Female Snorunt with the Dawn Stone evovles into Froslass.

3.Actually Electvire,Magmortar,Giratina,Heatran,Regigigas,Cresselia,Manaphy,Phione,Weavile,Magnazone,Lickilicky,Ryperior,Tangrowth,Togekiss,Yanmega,Leafeon,Glaceon, Mamoswine,Gliscor,Porygon-Z,Gallade,Probopass,Dusknoir,and Froslass are on the pokedex they just do not appear till you get the national dex because all of them either evovle from Pokemon on the national dex or are legendaries that do not appear on the map until the places they live are unlocked after you get the national dex. As for how you get them all go to this link http://www.serebii.net/diamondpearl/newpokes.shtml
And click on the name of the Pokemon to see where they are located.

Hope I helped!!!

1.List when getting national:
Diamond:
Seel
Dewgong
Scyther
Murkrow
Scizor
Larvitar
Pupitar
Tyranitar
Poochyena
Mightyena
Aron
Lairon
Aggron
Kecleon
Cranidos
Rampardos
Honchkrow
Stunky
Skuntank
Dialga

Diamond:
Slowpoke
Slowbro
Pinsir
Slowking
Misdrevus
Houndour
Houndoom
Stantler
Spheal
Walrien
Bagon
Shelgon
Salamence
Sheildon
Bastiodon
Mismagius
Glameow
Purugly
Palkia

2.Shiny stone-Togetic,Roselia
Dusk stone-Murkrow,Misdrevus
Dawn stone(female)-Snorant
Dawn stone(male)-Kirlia

3.Because they are national and they didn't want electibuzz in the Sinnoh dex.To evolve them you must trade it with a Electizer to evolve it.Same as Magmar,just it needs a magmarizer