Pleasure to help you. :) You can try sending a letter to the old residence... And address it to that guy. Perhaps the post office will forward it automatically. Either that, or check with the P.O.?
Another suggestion, you could go to the old residence, knock on the door. Explain your situation. Perhaps they have an address or a way to reach him.
Worse comes to worse, you can have a friend write you up a bill of sale and date it last year. The DMV usually doesn't question 1 year old bill of sale.