I'll going to be parting with all my factory stuff soon (don't know how quick you need it) but if you want to buy a custom harness it is going to cost a bit. The baddest place around is
http://www.thedetailzone.com/ for fuel injected wiring setups and/or your custom wiring needs.. I actually just saw a full 4.3 wiring setup on EBAY yesterday. That may have the piece you need. The guy sells all kinds of stuff so you can ask him - s10warehouse was the dudes name I believe... good luck