I stumbled across this
web page where it describes how you can build one for yourself. I was bored waiting for my new bike and the weather was awful so I built one. I spent something like $70 on materials. If anyone decides to go this route be aware that the bike spins really easily on this thing. I used my old bike as the tester but it would have scared the stuffing out of me with my new FJR. I think some of the changes I made helped and I've gotten very comfortable with it now. I turn the bike while seated on it but I imagine it would also work if I got off first.
These are a few changes I made/would make:
1. I added a thin piece of wood about 10 inches from both ends to help keep the bike from rolling off during the turn
2. Added a couple adjustable planks on the sides for the kickstand to rest on (need to permanently attach these someday)
3. I angled the ends of the plank to make them sort of like a ramp.
4. Had to use a 10" board to accommodate the FJR tires.
5. The place I got the bearing from has a version that locks after a 180 degree turn. You'd have to turn in opposite directions each time you park but it would ensure the turntable was always lined up properly and might make it more stable (though it hasn't really been a problem).
It's a little cheesy looking compared to the one in the original post but it works.
If anyone is interested in how mine turned out I can take a few pictures and post or you can PM me and I'll send them to you.