It might be cheaper to buy a broken 5000 series GPU of Ebay (with a compatible fan); I'd check it out at least.
i don't think that's a really good option. there are some broken 5850s on ebay for $50, but that's rather expensive for just a fan. just getting a new aftermarket cooler for ~$35 might be better, but that's still pretty pricey for a simple fan that should be ~$5