>>10830949We might need more info to help you out. How big of a terrarium are you working with? What are the "little models" you're looking at?
If you're working with the size I think you are you could probably just grab some 2" figures from moncolle or jazwares. If you care about scale just use the non evolved Pokemon that would look properly scaled next to each other. The ones like these
>>10829110 you can find locally. The ones in the attached pic are older Tomy figures, you can grab say Charizard, Blastoise and Machamp and they'd look roughly in scale.