I'm a bit old school but here's what I do... Get to know all your LGS's and pawn shops. Get in tight with them and before you know it they'll be looking for you. My places are glad to let me rummage threw their junk/spare parts boxes because....honestly how many guys out there are willing to throw cash at random/rusty/ what the hell is it? parts that the store wouldn't be selling any way.
Most of the time stores don't know what they have and I'll quote 1 of my LGS's " We don't have the time or the want to go threw all the boxes of stuff we aquire. So knock yourself out" You wouldn't believe how many times or different places have told me " since you know what it is
just have it "
I wanted to show off a box I just got a few weeks ago but....It just wouldn't have been nice. I got enough SKS parts from 1 box of stuff to build a whole rifle on a barrelled action. Cost me 6 boxes of cheap ammo
Granted it takes time and its a crap shoot if your looking for an exact piece, but its fun . Way more satisfiying than point and click. That being said...It takes me years to find some stuff and I could use a couple of good sites as well.
Still looking for a para-trooper cleaning rod...