Papercraft is used alot for diorama and military and historical modelling. They would be great for backgrounds and structures. There are a few websites out there that have paid and free models. I have seen some Transformers things in the past, but best to search online and see what comes up, as they are not common...more Gundam stuff is out there tbh. Paper Transformer or Card Transformer would be ideal to search. Let us know if you find anything of interest!