You don't happen to be local to north oregon/southWashington, by chance?  If not, I'll try some local hav places. Small would be good for me, because I have HF dust collector and dust deputy for the big stuff.

Call an HVAC company. They tear out old funaces daily and would sell you one. I have a 140 cfm small one id sell you cheap.

Nice. This has inspired me to do the same. Squirrel fan will be hardest for me to find cheaply.

I made an air filtration system for 15 dollars instead of spending hundreds