I've always thought these fan blades are the same as commercial refrigeration condenser fans.
Drop into either Actrol, Lovelocks or a commercial aircond/refrigeration supplier and see what they've got.
Add a couple of 12v motors and bracket. With your skills Dave I don't think this would be too hard. You might end up with a unit you want at half the cost.
Have a look at this link
http://www.americanhvacparts.com/p-1...n-cwfasco.aspx
