Quite often (But not always!) PSU fans are just common 120x120mm 12v fans. You may need to solder the connector though.
Poking around on the interwebz I found this:
http://images17.newegg.com/is/image/...23-S10?$S640W$
Note the text at the bottom left
Personally, I would recommend getting a decent PSU. I've seen a lot of mainboards, memory, and even videocards being blown out by a bad PSU. In almost all (if not all) the cases these were cheap 30$ PSU's.