Try UBG magazine, Classic Bike,Classic Motorcycle Mechanics and maybe MCN. Might be worth a look at e-bay too.
Prices? Could vary hugely from a few hundred quid for a box of bits in need of a nut and bolt restoration, all the way to £5000 for a mint, shiny matching numbers example.
I’d try to go for a tidy useable example that you could use rather than a mint bike that you would always be worrying about.