I cannot vouch for this site, as I've never bought anything from them, but as I'm always on the lookout for eBay alternatives, I thought I'd share with y'all. SoundsClassic.com
Oak Tree Enterprises has a huge selection of vintage gear and parts as well as restoration guides and general information on vintage stereo equipment.
I have had experience with Audiogon, and I can highly recommend them.
Where do you buy your vintage audio?