Hi Jay - I have the same stop - don't recall the maker's name, but he is an elevator engineer. Anyway, Bob Parcell came by, measured it, and made one out of micarta - works as advertised. Feel free to measure and take pics...
If it's the cam type micarta latch, look at the piece that mounts to the canopy rail. The guy has his name and phone number etched into plastic.
If you don't find it, I'll try to get it tonight while I'm at the airport.