What kind of parts are you looking for? Some are F3 parts are available from places like: http://www.uscamera.com/1nikon.htm
There was another guy who had lots of what I call "external" parts. He had a fairly comprehensive web store and ebay sales. I know he left ebay and I can't find his ebay store anymore. What's worse... I can't even remember what it was called. When I needed parts he was either a hero or a zero... which I found very odd.
For most parts, though, I'd be looking at ebay.