You can buy just a fan if you can find the right one. It's safer to buy a whole unit. The overclocker product sites used to have several. There was a thread here at OSNN about finding ATI replacement fans a year or two ago also.
Vantec, Thermaltake, Arctic Cooling have Vid card coolers. Fit may be an issue, especially for a 9600. The products are intended mostly for overclocking high end cards. If the cooler doesn't quite fit you may be able to use the fan out of it.