I have cast my own bumpers for years using the Smooth on products. It is very easy to make molds for most simple bumpers.
http://www.smooth-on.com/
You tint them with tintsall
http://www.sheffieldbronze.com/tintsall/
You can make a lot of nice colors. All shades of brown or reds what ever you like. I like dark gray but have made dark red that looked really nice. The molds can be made out of Delrin on the lathe in just a few minutes. The T type bumpers are the easiest but you can actually make anything. For the limited amount of bumpers the average cue maker uses it is no problem.