If one man's trash is another man's treasure, then garage sales and flea markets are full of trash. Garage sales are always the last-ditch means to get a quarter out of that which you have no use or value for. Which are often things other people greatly value: typewriters, turntables, sewing machines,VCR's, and other anachronistic things those guys on American Pickers somehow turn into a thousand dollars. And some people have no value for the records they used to listen to when they were younger. If they were more patient or proactive, they might realize a greater deal of money can be made by listing each record on Ebay. But nonetheless, their ignorance is your bliss. Thumbing through some of these scant boxes may turn some surprising results.
Gemm predates Ebay and Amazon, starting in 1994 when the internet was still in diapers, and it's main purpose was to miniaturize the world and make that tiny world a dedicated marketplace for music. The emphasis has always been strictly about music, first and foremost, and still is today (in addition to everything else you can find on Ebay and Amazon). So with a track record that deep--imbedded at the very forefront of the internet's earliest global gazes--you can expect to find anything in the world your heart could possibly want (and want to listen to).
In these days in which record store chains are largely endagered, if not completely extinct, there are a lone few that still perservere. One of them is the New England-based Newbury Comics (the original location still stands on Newbury Street in Boston, MA). There amongst the graphic novels, used DVDs, keychains, and other assorted novel intrigues is proof that the vinyl industry is still alive and well. While the used selections leave a lot to be desired (most of it is sold through through their Ebay storefront), the big draw is in their collection of new releases; just as any record store would make sure to be stocked with the latest CD releases (the equivalent of iTunes and its digital releases), Newbury Comics is adamant about stocking the latest vinyl releases as well. No format left behind (except cassette tapes..and 8-tracks...and wax cyllinders...okay, you get it). This is very exciting for the vinyl community, knowing that they can keep their days intact of when they used to get excited about rushing to the record store on the day of an album release and pull a slick, still-wrapped LP from off the shelf of a physical record store. You can't compress that feeling.
Amazon sort of takes the reins on the idea of a internet marketplace; after all, you can acquire virtually everything you can in person at a phyical storefront (and some things you can't). In that mix, of everything in the world made-to-order, is vinyl records, new and used. If you can't find a record you are actively seeking anywhere else, you can probably find it there. And Amazon tends to have cheap shipping costs (free for orders over 25 dollars, with participating items that is).
While thrift stores may be the ultimate hand-me-down store, inside houses the possibility of some awesome vintages being handed down. Aside from clothes that look straight out of the Brady Bunch, there are the occasional, obscure treaures; sometimes a stylishly worn-out denim jacket, and sometimes a really good record album. Most thrift stores have a section devoted to music, particularly old vinyl people donate for lack of personal value. With that you get a lot of classical music records, showtunes, big band stuff, but sometimes you'll get something really awesome between all the dust and beat-up cardboard. The thrill is in the hunt (and isn't it always?).
Not some streamline, glossy chain, but rather a humble establishment that's a little more presentable than a storage locker, local mom and pop stores can be found scattered about. It's your job to look up the nearest location to you (usually in any major city, or well-populated town), but once you find one, it's usually akin to finding the pot of gold at the end of the rainbow. Within you are likely to find a modest number of employees (perhaps just the owner and an additional helper), all of which care about the music they deal and are amateur experts on. And as everything is second-, third-, or eighteenth-hand, prices are guaranteed to be incredibly reasonable; e.g, just ten bucks can get you three decent albums, where it might only pay the shipping and handling of one online. For any pre-90's album, your most cost-effective means of acquiring it is most certainly in some shanty hole in a wall, where human decency dwells.
This site is a piece of common ground for a world that loves music. A bit like GEMM, Music Stack consolidates the best of what the world has to offer, in accordance with what you are looking for, and neatly organizes it into a itemized list from which you can compare formats/prices/conditions/etc. Music Stack as a third-party intermediary of sorts stands between stores and buyers all over the world and ensures smooth transactions (as Ebay does). Make sure to keep this bullet in the chamber as you scope out your next record. Bonus points: they accept Paypal (which Amazon has still yet to embrace...in this day and age).
Ebay is a great place to find anything you could possibly think of, sold by some person who could just use the money. And then of course there are the independant businesses who list items on Ebay as a sort of virtual storefront. There's a little bit of both of this when it comes to vinyl records, and a whole lot of what we call "fishing," where someone asks some unreasonably outlandish figure for a record, grounded in no empirical research or true appraisal work. They just want to dupe someone who thinks every record from the sixties is rare and worth hundreds of dollars. In reality, old records are as cheap as the condition they are in, as common sense should dictate. Always know there are myriad other means of acquiring a record that isn't at the first place you searched.
All that said, the auction format is very much conducive to serendipity and good luck, as sometimes you can score a really good deal at the expense of another bidder's distractedness/lack of ambition. Ebay's biggest flaw? Wild shipping fees, and the extra-inflated prices as a result of the seller fees they charge.
Here's a great place to find just about any record you can think of new and used, boasting a collection of "over 2 million fine records." The store has a noble origin story, readable on the site's 'about me' page, in which one vinyl-lover in the seventies (named Craig Moerer) went on a road trip collecting vinyl, which he filled a record store with. Inevitably, the store expanded its horizons in accordance with the digital age, and now deals vinyl on a global scale (What a success story!). While Records By Mail also deals through a lot of third-party vinyl databases, its own website boasts both selection (new and used, of every genre/decade) and relative affordability, not so much disposed to gouging browsers without good cause.
Heaven on Earth for vinyl-devotees, this store is surely the biggest chain on the West Coast. It doesn't try to hide behind its unabashed vinyl-mindedness, or hide behind walls of inane novelties in fear that vinyl might not be enough to maintain steady business. Rest assured, Amoeba lines its walls 12" at a time. At every opportunity, the store celebrates the spirit of vinyl, with promos and in-store performances, all to keep alive an important tradition, the idea that not all forward progress happens in the right direction.