Thrift stores, flea markets, and tag sales
My sister works part-time at the local thrift store and recently hooked me up.
Someone donated a box of stuff and in the bottom, her and a co-worker found a handgun. Fortunately, they both own firearms and didn't blow a gasket or freak out. Sis ain't quite the firearms afficionado that I am, but she can read and knew right away that "Crossman Repeatair .177 caliber" means it was a BB gun. She showed the gun to the owner (It's a private store) and stated that "My brother the gun-nut will be interested in buying this if it's OK with you." To which the owner replied: "Just give it to him. I don't want to deal with it." Needless to say, I'm now the proud owner.
I had to buy some 12 shot cylindrical magazines for it before putting it to good use as a plinker for me and the kids...
I've found some good second-hand deals throughout the years at tag sales and the like. I still think back to the simpler times of pre-9/11/01 like when the Newfane Flea Market still allowed firearms sales and I wandered the entire place with a shotgun that I purchased at the second or third stall.
A Keystone arms bolt-action 12 gauge with fixed two round magazine and select choke for $60.00 The finish was in horrible condition, the stock was dented and scratched, and the bore was rusty. It came home as a rainy day project, but quickly turned into another loving restore of an old gun.
I did a complete scrub of the barrel and was amazed and relieved to find that the rust in the bore was only surface and hadn't been there long enough to cause pitting. I did a complete re-bluing job and then used a steam iron to suck out at least 90% of the stock dents. I sanded the crap (literally!) out of that stock and then gave it a few coats of polyurethane. She now resides in my brother's collection as a fine specimen of magazine-fed bolt-action shotguns and doubles as an early example of select choke systems.
I made some money off it and got another restore under my belt.
It shoots like a champ.
I also once found a circa 1950's Outers gun cleaning kit with everything, and I do mean everything, intact for $1.00. The solvent bottle was opened but still full and everything else was untouched.
(P.S. hope this keeps this post here!)