Here's a parts blow up for the TZ throttle with Yamaha part numbers, all available there except the #7 tube. The tube may be available at other places, found by Googling "Yamaha part 5F7-26243-00-00"
Bill
http://www.partzilla.com/parts/search/Yamaha/Motorcycle/1982/TZ250J/HANDLEBAR%20-%20CABLE/parts.html#