These guys have a full defroster kit, which includes a wiring harness and timer switch/relay. They don't list the wiring and switch separately on their web site, but I'm sure if you called them and explained your need for it, they could package one up and send it to you...
Frost Fighter Defroster Repair and Replacement Kits
I'll probably be asking them the same sometime between now and the fall, as I have a hard-top with a defroster. I also need to bond the tab back on, and the ludicrously priced permatex adhesive didn't take, so hopefully their 2-part stuff will...
