I'd be curious if there are more on the road now than there were, say, 20 years ago. Sure they're older, but as Donn and Frank (spritenut) show, folks are bringing back ones that would have been considered hopeless not too long ago -- maybe the numbers are going up.
There are a couple of different registries around, but none are really definitive, and they are not (so far) all that easy to research.