http://www.ynzyesterdaysparts.com/homepage.htm

http://www.narragansettreproductions.com/wiring-harness.html

http://www.riwire.com/

Chevs of the 40s, Classic Part, The Filling Station and Jim Carter (and probably other reproduction truck parts vendors) sell braided wiring harnesses. Most likely they source them from one of the three other companies listed above (some of the other companies above might be sourced by another company above).