A. There are a couple of options. Check with motorcycle salvage yards, and ask if they have one you can get used, check with your Yamaha Dealer to see what a new one would cost, or check out this page I found for information on getting yours reconditioned (and if you have one of the type that can be reconditioned)
The TCI on the 1981-1983 looks like the one below and cannot be reconditioned. Check with CyclePsycho to see if he has a used one and can help you out.