What makes you think you need one? I looked at your system and it appears you have enough space between the components for them to cool normally. If you still need something Corsair makes very quiet cooling fans.
Quiet Amp Cooling Fan
Can anyone point me in the direction of a VERY quiet fan that I could use to increase airflow over my amp? I know about the Parasound Zbreeze, which is now discontinued and also too noisy. A really quiet version of something like that which sat atop the amp would be fine or even a small circular fan which could be mounted to the vertical pole of my rack might do the trick. Any suggestions would be greatly appreciated.