I found a part resource for heated seats. I'm not sure what they would be missing, but here are the basic components:
Seat cushion heaters:
http://www.trademotion.com/partlocat...08&catalogid=2
Seat back heaters:
http://www.trademotion.com/partlocat...08&catalogid=2
Heater switch:
http://www.trademotion.com/partlocat...22&catalogid=2
Those components alone are about $600. It would be worth going aftermarket if you could use the oem switches imo.