Try bus/heavy truck dealers in your aera. I got mine from a dealer who was selling new busses, they took mine in on trade. Maybe check the phone book in your aera & call the heavy truck and bus dealers & ask.
I went to a few auctions (not government auctions) and seen busses going for 2 or 3 times what they would normally sell for.
here is a link to the auction I went to http://www.422sales.com/