Google for "mold your own rubber parts" or "cast your own rubber parts". Lots of lousy videos on YouTube on how to mold rubber parts. I use Plaster of Paris for the mold, Devcon Flexane 94 Liquid 15250 two part urethane rubber and Vaseline or silicon grease for mold release. Careful when storing the stuff as the stuff in the bottle attacks the bottle and causes it to leak. It cures in 10-15 mins, so be prepared to work fast. Although it's made for making flex molds, it's also the right stuff for making fairly hard rubber buttons, gaskets, shock mounts, seals, etc.