Sourcing the exact correct fan (or fan spec.) is potentially going to be pretty hard if neither Sapphire nor Google are going to tell you what it is. You might have better luck sourcing a cooler + fan combo. Something like this
(which wants Arctic Alumina or so I'm told
) might be pretty good if you have room for it. If you are over-clocking you might want to just get rid of the fan it comes with and go with something louder.
In my experience these fancy looking coolers are not just bling -- they actually work (albeit with widely varying degrees of efficacy). You might find you are able to squeeze a but more MH/s out of the card with a big nasty radiator on it like that although I don't have experience with recent ATI cards so... maybe my advice is worth what you paid for it