Been following this thread with great interest. I'm going to have to replace the stock rad in my car with a Fluidyne or PWR eventually, so when I saw a Koyo rad cooling a computer I was very impressed!

Anyhow, I guess you've already moved on from finding an Automotive fan but the most popular aftermarket rad fans are from Flex-a-lite or FAL fans for sport compacts. Here's their website http://www.flex-a-lite.com/auto/html/electric-fans.html

Funny thing though, the stock fan shroud on my vehicle has been shown time and time again to be more efficient than these electric fan.

If I wasn't a total newb to watercooling, I'd consider finding a car radiator for passive watercooling as well. My HTPC is in my theatre room, and the A/V wires come through a wall from an unfinished room. I want to setup a slient watercooling system where the radiator and pump is located in the other room.