i would google that for your particular area, however i dont think you would be finding any gems from the recyclers. craigs list or ebay would probably be a more decent bet for finding a pc. also if you just want something to tinker around with, the raspberry pi looks really neat http://www.raspberrypi.org/
its a mini linux running computer that you can program to do pretty much anything you want.
PC recyclers usually recycle the computers they get. i.e., stripped down, appropriate parts shredded into dust-like pieces, others tossed into various boxes for shipping.
You probably won't find a computer that's in one piece at a recyclers. And if you do there's almost definitely something wrong with it (to be recycled in the first place). It's not worth the trouble.
uhm... I have Pentium D 3ghz (ebay) on ECS P4m800 from garbage
Celeron 2.8ghz on some other mobo from garbage
Athlon x2 2.2ghz not from garbage
Pentium 4 2.6ghz from garbage
Celeron 2.4ghz from garbage
Pentium II 266mhz from garbage
Pentium III 450mhz from garbage