Hi.
I've got a Nvidia GTS-450 graphics card and use it since many years, but the past year its fan got broken and then I had to attach an emergency fan. I searched a lot online about a replacement but I didn't find the exact one and the original fan is discontinued. Tired of the "emergency fan" I decided to convert it into an "original" fan.
Unscrew and remove the case of you GPU and select your preferred method to attach the fan to the cover. In my case I used a cheap glue because I had nothing better at that moment. It is important to press and hold the both elements for a while to be sure they glue correcly.
This is not a very recommended method because the GPU can reach very hot tempreatures inside and a wrong glue can weaken with heat.
Once the case and the fan are tightly joined, screw the whole case into the dissipator (this can vary a lot between models and brands) and you are ready to mount your restored grpahics cards into your PC!
Because this fan isn't designed specifically for your GPU, it's possible that it moves less air. It is better to connect it to a Molex or fan pin on the motherboard. If your fan doesn't have any speed reculator it will spin at maximum speed, but if it does you can use specific software like SpeedFan to control its speed as you want.