Your best bet would be to buy a sheet of lexan. Take some paper to make templates of the shapes with and transfer that over to the lexan. You can then cut the lexan out and install them in the game. It's easiest to cut with scroll saw but I've cut some with a jigsaw and dremel before.

You can paint the underside of them to make them different colors if you'd like or even tape artwork to them if you find something you like. That's really going to be the easiest way to accomplish what you need.