I don't have any suggestions for a completely different alternate replacement, however I'm going to use this thread to help the community get matching fans for the original.
Someone on eBay recently posted a large quantity of correctly matching original generic heatsink/fan combos for these cards. The only thing you would have to change on them is the plug. (You could also remove and re-solder the entire cable from the fan itself so you'd have no visible wire patches.) The bid price is for two pieces, and at only $11.00 US plus shipping it's an absolute no-brainer. I bought two packs of two (four fans total) but there's 53 two-packs still available. (Why they come in factory-sealed packs of two I have no idea.)
http://www.ebay.com/itm/311574316455?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT Even if you don't need the heatsink you can still extract the fan and transfer just that. These generic heatsinks come with a blank silver badge plate (with protective blue film), and because they are exactly the same layout you could unscrew and transfer over the original nVidia badge plate for autheticity's sake.
In the case of my own card the fan is still working and quiet, but I can tell it's getting stiff in the bearing. I tried to detach the fan only but found one screw to be completely jammed, so finding these heatsinks complete was a god-send. I haven't switched it over yet but I'm posting a comparison photo for your reference:
Get them while you can even if you don't need them yet - you might never get another chance to find these brand-new. All owners of these collectable cards should own a spare fan.
BTW, are the original heatsinks just thermal-pasted on? I don't want to risk tearing the chip of removing it. Has anyone tried using a heat gun to break the bond with the paste on these cards?