Well, you could look on Ebay for 8600GT fans and then there are these manufacturers that make high performance heatsink&fans for Video cards like Zalman but then you're looking at a price tag of 30-40$, like this one for example, listed to be compatible with the 8xxx series of Nvidia including the 8600GT)
http://www.zalman.com/global/product...ad.php?Idx=374
(scroll down for compatible VGA cards and you can download the manual for further inormation)