I see a few around, but don't have any myself. got any pics?
You should also probably use a ring with "more" teeth than one with "less" (exactly what more nad less are, I don't know). You want to limit the angular separation between teeth so that you can always be sure that you have good tooth engagement in the chain, to hold the ring in place. At the same time, more teeth = more friction. It could also have some lateral sway that would annoying.