Was able to purchase the fan from http://allpartsmac.com/
Make sure to remove old adhesive tape from both the iMac *and* the screen before putting new adhesive tape on.
- Consider carefully vacuuming the dust out of the fan base before installing the new fan.
- Make extra sure not to drop the T10 screws into the iMac when you put them back.
- Make sure to remove the adhesive tape from both the iMac and the screen before putting new adhesive tape on.
- You'll need to reset PRAM when you turn the iMac back on.