Theres a big write up on them and the RC30 in Classic Motorcycle Mechanics june last year, I've got it somewhere if you want a copy of the article. There a guy who breaks them (sound familiar? ) who seems to know the whereabouts of loads of them!
I mat be wrong, but i'm sure i also read of some of the factory bikes being registered for the road too, that would bump the numbers up a bit. Still not loads though. Might have exaggerated that a bit

*edit* just glanced at he article now, and a fella called Peter Day is the man to speak to if you want a good 'un!