mm- no one source. Discogs is a decent starting place, but grading and pricing is all over the lot. For stuff like Warner green labels, many can be found in bins in used record stores all over the U.S. The Steve Hoffman forum is a good place to get a handle on some better known pressings of "classic rock"- just run a web search for "best vinyl pressing of X" (where X= band or artist or album title) and you'll probably wind up in one of the Hoffman threads. (Don't take anything on faith, but the better informed threads usually involve comparisons of different pressings, and rarely conclude that there is "one" best). I've gotten records from all over the world, and do rely on a few established dealers, but like many people buying used records, I also bid in on line auctions. You need to do your due diligence on pressings- some of the descriptions are not always accurate, and as I already mentioned, I tend to take grading with a grain of salt. (Visual grading tells you the record looks good, that's pretty much it-aside from play grading, which is also subjective, ask about warps). Part of the fun is the discovery, the research and the chase, rather than one stop shopping.