I'm wondering if something like these ones can be used for DIY something similar to your GM20 .....
Rotary Solenoid 24 VDC 30 degree. Lot of ten pieces - eBay (item 290376984632 end time Jan-01-10 17:45:53 PST)
Anyway, the seller don't say if they are bistable, and for make optic switches, the solenoids must be bistable or have a self-return spring inside, at least ..... other than this, you need to build all the rest, so, don't know if it worth the effort ..... i mean, for someone with machines and free time, it can end in a funny work, but if you need to ask an external worker for all the parts, it may end in a too high price .....
Sorry, those are just some of my crazy ideas