There 30 Chinpokomon dolls throughout the entire game and there quite a few missable ones since the area they're located is limited only to certain quests. After successfully collecting all Chinpokomons, the Chinpokomon Toy Corporation will be added to your Friends List.
1: Chu-chu Nezumi
On a tree west of Butters' house.
2: : Furry Cat
Beside a tree, to the right of the Broflovski residence, right before reaching Kenny's house.
3: Lambtron
Second floor of Tower of Peace. You can find it hanging on the right side.
4: Monkay
Inside Butters' room, near the window to the right.
5: Pengin
Found in Cartman's garage
6: Shoe (Missable)
In the main mission "Beat Up Clyde", you'll reach a part of the tower where the gate is operated by two wheels located inside the smaller towers on either side. Teleport to the upper balcony to reach it.
7: Accountafish
Found in the small newsroom vent. You need to enter the vent after using Gnome Dust
8: Vamporko
Found in the basketball court east of the Community Center. You need to use the alien probe on the wall to teleport there.
9: Fetuswami
In the quest “Unplanned Parenthood”, you'll reach a part where you have to destroy an auto-turret. Shoot the grenade the nearby dead soldier is holding to blow the corpses up. Once the path is cleared, enter the hole then go to the left to reach the chinpokomon.
10: Gerbitoad
Right outside Mr. Hanky's house in the sewers
11: Gunrilla
Found on top of the storage cabinet in the left side of the conference room inside the military/ Taco Bell headquarters.
12: Gophermon
Found in the left-most cubicle of the Community Center's bathroom
13: Sna-Kat
On a tree west of the town hall.
14: Mouse-Tik
Beside the chest in the girls' Sparkle Chamber. You can access this after completing “Recruit the Girls” quest
15: Poodlesaurus Rex
You can get this earlier during the quest "Detention Sentence" by shooting the vent grate on the ceiling in the first hallway. You can find it inside the vent past the cafeteria during the mission “Attack the School”. Finally, if you have sided with the humans, one of the goth kids will pick the door to the kitchen, making it possible for you to come back for this chinpokomon if you missed it on those quests.
16: Roo-stor
Inside Professor Chaos' lair in U-Stor-It storage. You need to get the Chaos Lair Key from Butters' room to access this. U-Stor-It will be locked on your first visit. You have to hit the ladder above the dumpster beside the hobo/street merchant then climb up to the advertisement to get inside the fence. Enter the office building and hit the switch there to permanently leave the gates open.
Once inside, go north then east then open the right-most storage. The chinpokomon is located on top of the vent.
17: Donkeytron
Inside an oven in the school kitchen. You can access this at the start of the main quest “Attack the School” As soon as you enter the kitchen, turn the stove on, go to a short distance and use Cup-a-Spell to blast the oven, freeing the chinpokomon inside.
18: Stegmata
Inside the Broflovski Garage
Once you have access to the Elven Kingdom, exit through Kyle's house and go upstairs. Find the key inside his parents' room.
19: Fatdactyl
On top of the ticket booth in front of the cinema.
20: Ferasnarf
Once you have access to the Community Center as part of the story, talk to Mr. Mackey and get the quest “Wasted Cache”. Next head Mackey's storage shed in U-Stor-It. This can be found on the top shelf.
21: Pterdaken
After reaching the second floor of the school, head to the southeast hallway and open the unlocked locker to find this inside. Shoot it to collect it.
22: Biebersaurus
After learning Nagasaki, return to the cavern where the crab person and the fruit bat is located. Break down the rock the pick up this chinpokomon along the way.
23: Brocorri
This chinpokomon is found encased in ice in front of the Tower of Peace. Use Dragonshout to blast the fire off the lamp and defrost Brocorri.
24: Velocirapstar
Found on the second floor window of Token's house.
25: Flowerpotamus
Found on a shelf in Skeeter's Bar
26: Beetlebot (Missable)
While inside the alien ship right after freeing Randy Marsh, you'll have to power up the second elevator using the White Power Crystal. After disembarking from the elevator, you'll find this on top of the monitor screens to the right.
27: Cosmonewt
Use the alien probe tool to interact with the teleporter device the reach the submerged UFO containing this chinpokomon.
28: RabbiTech
This is found in the upper shelf of the Police Station's Evidence Room
29: Roidrat (Missable)
This is found on the attic while finding another way to The Bard's locked room during the quest "The Bard"
30: Terribovine
This is found under the bench in front of Tweek Bros Coffee. You can reach it by shrinking yourself using Gnome Dust.
Poodlesaurus Rex is also missable if you join the Elves. Your description even says so.
Gunrilla can be missed but later on in the story
Gunrilla is also missable.
I think Fetuswami is missable. Cause once you've defeated the Giant Nazi Zombie Fetus, I don't think you can go back, and get it.