For air any squirrel cage blower with an adjustable flap to restrict intake will provide excellent amounts of air.
Like this one? The motor I bought for my lathe had a blower attached to it.
I have to remove the pedals and replace them with handles and tighten up
the chain a little. Then make a connector to get the air flow into the forge.
Ther is a little more work done than I have photos for... I added a brace
the wooden pulley. I might have to replace that pulley with a larger one
if I do not get enough air flow. I think I get around 30 revolutions of the fan
cage for one turn of the pedal/crank... ( do not remember exactly )
Getting back to this one is almost to the top of my backlog of projects....http://s147.photobucket.com/albums/r295/ConalOhAirt/Forge%20blower%20project/
I have an electric fan on it now but it is so picky I have to fiddle with it so
much it gets annoying.... I might try to work out a way to attach both the
electric blower and the hand cranked so I can pick and choice. For welding
temps I might need the electric blower..... I'll have to actually get this finished
to find out how good a job it does.... lol