They come up every once in a while. I saw a set on eBay 4-5 years ago that went cheap. I didn't have a drop lock at the time so it didn't matter. Now I do and wish I would have bought them when I had the chance.
I think the chances of fitting another gun would be about like the odds for a set of barrels from a different gun fitting. There are 2 distinct styles of locks for a drop lock. Some have integral firing pins on the hammer and some have bushed firing pins in the action and a flat faced hammer. Sure there are other slight differences in the ~120+ years they've been made.
The market may be pretty narrow, but they are cool regardless.
