The Apple part number is actually 922-8202. The next 20 inch iMac has a different part number for the fan but the images in the service manual are identical. I would be surprised if they were not interchangeable. The early 2009 version has a different label but again I would be shocked if it didn't work.
Mid 2007 922-8202
Mid 2008 922-8510
Early/Mid 2009 922-8843
PowerBook Medic also lists 922-6993 as an interchangeable HD fan for a 20" iMac. That one is from the Late 2006 model.
It looks like any 20 inch Intel iMac HDD fan will do to replace yours.