Some websites for used macs and parts:
www.nexcomp.com - has 30 pin SIMMs and ethernet transceivers
www.preowned.com
www.welovemacs.com
home.earthlink.net/~mccomputer/

I bought a Quadra 700 and a Sony monitor from Preowned. Haven't dealt with the others.
BTW, anybody know if those $29 Radius grey-scale full-page displays Preowned is selling will work with NetBSD? 

And ebay has all kinds of stuff from Apple //c power supplies to PowerMac motherboards. Yahoo and Amazon also have auctions but there's a lot fewer items. Fewer bidders too I would guess, and that may be an adavantage for buyers.