I acquire most of my K6 and socket 7 hardware from Ebay but some things I've had for years. Some internet venders, but not many, still sell some K6 hardware but they're usually overpriced. You may get lucky and find some older hardware at a Computer fair or flea market.
I usually find such stuff @ swapmeets (enthusiast flea markets), eBay, people tossing out their old PC gear/upgrading OR in the clearance bin @ a PC builder's store
Speaking of which... I may soon inherit a 80386 class system as part of an upgrade exchange deal for one of my refurbished PC's (1Ghz Celeron Netvista), should net me a few needed dollars too into the bargain