I decided that rather than spend $120+ from aircraft spruce, I would roll-my-own avionics cooling fan. I started with a good quality brushless ball-bearing squirrel-cage fan and made a backing plate out of aluminum. Bent the aluminum to wrap around the output section of the fan and radiused the fan to match the raduis of the bend. I match-drilled the two together for 3/16 bolts. Now I just need to add a couple 5/8" exit ports and I am good to go. I will also put a bit of sealant where the fan and alumnum meet, but they are pretty well matched already.
