I'm gonna put a fretless neck on my jazz bass. Where the best place to look ebay isn't turning up much nether is talkbass
Warmoth will build one to your specs, but it will be on the pricey side. It will be worth it, though.
"Maybe this world is another planet's hell?" - Aldous Huxley
Look into Allparts or Mighty Mite.
Composite Aficionado

Spector and Markbass
Try putting up a "WTB" (Wanted to buy) thread in the TalkBass classifieds. A lot of those guys will have that kind of thing lying around and don't think to sell.
I'm not sure if you have to be a supporting member to use the TB classifieds though, and IIRC the donation is pretty steep.
Fender Precision Bass
Fender Jazz Bass
1967 Fender Coronado Bass II
Warwick Star Bass
Squier Precision Bass TB