Super cool! I recently discovered Ponoko will laser cut/etch silicon. You can get 3 overlays out of the 15x15 sheets, but they seem pretty thin (.06 in/1.5 mm). I suppose you could buy some raw silicone that is thicker and use it as a backing material. Neoprene could also work as a backing material, but might be hard to bind to silicone (cyanoacrylate or super glue might work).
Depending on the design (aka machine time), it would probably be around $100.
I haven’t used the service yet, but good to know about.