This thread is pretty much seeking the holy grail and there's multiple versions of it, plus frequent asking on other threads.
The truth be known, intel on here will only get you so far, if there's a verified big and busty rack on offer in a shop then lurkers will make her busy. Also, sometimes people on here claim they've seen a massive pair when they're just decent rather epic.
In years gone by I was well served by just recce'ing, making it my business to tour shops and see what I saw on offer. None of this taking who's offered and hoping for the best, going out of my way to see who actually works there and if they're packing. The downsides to this approach is perhaps you go on the wrong day, perhaps someone who's potentially blessed with big naturals is busy or hidden from view etc. It also takes a lot of time and effort really and shops don't like it because you're bothering them and not booking. Not for nothing do they lock doors and have signs in the window with their prices saying no booking, no entry.
