Any high static pressure 120mm fan will work. It needs to be high static pressure. Otherwise it will have trouble pushing air through. Given the limits of the heatsink design. I wouldn't waste money on an expensive fan. It will add very little cooling performance.
The Arctic F12 PWM is quite good. It should outperform the original heatsink fan and is quite cheap. It actually performs about as well as the Noctua NF-F12. A fan that costs three times as much. It regularly outclasses fans that cost two to three times as much. It is also one of the quietest fans on the market.
http://www.overclockers.com/pwm-fan-roundup-twenty-four-120-mm-case-fans-tested/
https://www.amazon.com/ARCTIC-F12-PWM-Rev-Dynamic/dp/B00H3T1KBE/ref=sr_1_1?ie=UTF8&qid=1494506899&sr=8-1&keywords=arctic+f12+pwm
It is also sold in a value pack if you want to soup up your case cooling. A tremendous value. They can also be daisy chained.
https://www.amazon.com/F12-PWM-PST-Value-pack/dp/B00NTUJTAK/ref=sr_1_2?ie=UTF8&qid=1494506981&sr=8-2&keywords=arctic+f12+pwm