I have been using a small 25 cuft/min blower that I bought from Surplus Center. It's a small plastic centrifugal blower. Unfortunately is is now not working because it got over loaded with titanium dust.
I bought a turbo charge off of ebay. Buys said the turbine was a bit cracked. I have disasembled it and pulled out the compressor.
The compressor is about 2 inches in diameter. Full speed rpm for this turbo charger is maybe 30-40,000 rpm. However that is at a large boost over several psig. I only need 5 inches at most. Rough calculations seem to indicate that a small fractional hp dc motor running at 3000-5000 rpm should be enough to provide the pressure boost I need.