Where can I get these fans?
 

I heard these were common, but I'm not sure what type of fans they are called.

those are axial fans.. Grainger or Mc Master carr

try the auction site,,, 239 cfm was cheap,,, search axial fan.. don't rush on getting them,, I have seen them on there for $20 and will combine shipping,,,,

I saw some on Burden Sales surplus center
prices looked reasonable

Thank you.

Ditto, I picked up 12 of them. Great deal. If I get a chance, I have been meaning to put up a pic of what I did with one. I put it on my mosquito magnet. I put a tube around it with a screen and it sucks in so many mosquitos you wouldn't beleive it. My magnet works incredible anyway but I always noticed bugs attracted to it and swarming around now they get sucked in.