Most barbecue wood is purchased from firewood dealers, but make sure that you let your relatives, friends, neighbors and co-workers know that you are always looking for fruit woods and hardwoods. Let them know what size you might need. As an example, if you let them know that even trimmings would be nice, you can collect a quite variety of wood types. You will be surprised at the number sources that turn up.
If you cannot find a source of barbecue wood in the yellow pages, go to a barbecue joint or restaurant in your area that uses wood and ask them where they get their firewood. They will be able to tell you what kind of wood is available and where to get it and how much they have to pay for it.
Also, check out this Web site for detailed information on how to buy wood from a dealer.