Yes, I agree. There is no garantuee that a tame bird will get another to calm down. After the 30-60 day quarantine period, the birds may end up hating each other. This bird has had to depend solely on himself and needs to remember that people can be trusted again. I would just work on sitting near the cage, talking to him and reading out loud to him. Get him used to your presence.
After 15 minutes each time, put a treat like air popped popcorn, nutriberries, a few plain cheerios, or an avi-cake square in his dish and praise him. When he is no longer fearful, then you can work on him taking the treat from your hand at the door of the cage.
This of course is just a start. My site has some great article links on taming and training birds.
http://www.christiessite.com/birdlinksHowever, like mytielwoody said, PLEASE advertise on the internet sites around that you have fund a bird. There are many parronts out there that are heartbroken with the loss of their baby. There is a lost and found section here, a few links on my site, and put an ad in your local paper. You can even call the vet's offices in your area to see if anyone is looking for a lost tiel.