The plastic of the Roman Empire was perhaps ivory... maybe something like this can be made artificially now?

Just what is ivory anyway? It's teeth in some kind of plywood like structure:

https://www.sciencedirect.com/science/article/abs/pii/S17427...

Some plastic things can be directly replaced with it:

http://www.antiquegamblingchips.com/distinguish_iv_bon_cel.h...