Every dead gas hot water heater has a nice little blower in it.
A friend tells me that he simply goes to stores that sell new water heaters and asks to be allowed to either take the blower out or to take the whole thing home. He has done this many times. I think the blower is used as a "power vent". He builds coal or charcoal forges as donates them to our club's raffles/auctions. You can use an air gate to control the blast so you don't have to worry about speed control. These blowers also work well for gas forges.
I look for small blowers too, when I go to garage sales or auctions. Often they will be in a box of misc. stuff. If I don't want the whole box, I just deal with the buyer. I usually get the blower for a dollar or two.
Pete Stanaitis