Levhian,
Looking at the pic from Igor's post, you may need to cut off the connector of the old fan and splice it onto whatever new one you purchase. Additionally, it seems you'll want to get a 4 wire (PWM) fan. Also, the below comments are assuming the mount holes are indeed standard. If not, some plastic, CA glue, and a dremel or the like to may be needful.
For a case fan, the Noctua route is surprisingly affordable:
Noctua NF-B9 redux-1600 PWM, High Performance Cooling Fan, 4-Pin, 1600 RPM (92mm, Grey) - $10.95
https://www.amazon.com/Noctua-Bearing-N ... B00KF7S9F6For heatsink use, that's where the Noctua route gets expensive to the point where you may wish to consider a cheaper, alternative route e.g. Scythe, Be Quiet, Cooler Master, whatever. Here's a somewhat random example of what should be a fine option to consider:
Arctic F9 PWM - $7.49
https://www.amazon.com/ARCTIC-PWM-PST-C ... B00H3SVWF4Edit: In looking at Igor's Amazon link again, that fan's mounting hole pattern may be 80mm (even though the fan is 90/92mm). Levhian, could you measure the distance between the holes in millimeters?