Prague.
Used to be good in immediate post-communist days, not been there for years though
Prague is not worth a visit purely for punting these days. As to blondes, a quick check on Annonce shows 376 small ads for Prague, of which about 100 claim to be blonde (but a significant number obviously aren't from the photo).
As I have said before, London takes a lot of beating. For example, taking just one agency, Diva has about 120 blondes.