Check out a craft store ....something like Hobby Lobby. Usually you can find a pretty good sheet of color acetate for cheap and cut your own circles.
Hobby Lobby does carry colored acetate in several colors. You'll find it in the same area as the hobby knives and resin casting supplies, usally the nest aisle over from the model cars. You may need to double up the sheets to get the color right, though. Another option would be to use regular clear sheet plastic, then paint it with a transparent model paint. That would allow you to control the color a bit better. I did that to make new turn signal indicator lenses. I did change the color from green to blus in my case, though.
