In the UK, I would highly recommend
http://www.blowers-jewellers.co.uk/
They have a mix of vintage, relatively new (so dated late 90's to mid 2000's) and current (some new and I am assuming grey market at big discounts).
Incredibly, they give a full 7 day no quibble money back guarantee. No reason needed plus a year's guarantee .
They currently have a very nice 74 Daytona 6263 case No 402*** with Sigma O T SWISS T O silver dial with black subsidiaries
.