You would have a very difficult time just replacing the fan on the gpu.
Set the fan speed to 60% and you should be fine while gaming
(use MSI Afterburner or EVGA Percision X)
Replacing the evo fans is very easy and only requires new fans and the old mounting brackets/extra that came with the cooler. Fans should be 120mm.
Check out Frozencpu.com / Xoxide.com / Newegg.com / Amazon.com for fans
Aerocool/Scythe/Gelid/Phobya/Silenx/Noiseblocker all make excellent fans with great dba/cfm and colored/leds.