Netgear does not sell parts. You'll have to look for a standard PWM fan with similar specs. Maybe somebody has already done this and has a suggected model. But what I wanted to point out is that the connector pin order is non-standard. See ReadyNas-pro-6-fan-stopped-working . I'm not sure why nobody suggested in the post that the pins simply be removed and re-inserted in the new order, which is usually pretty easy with a fan.
Once you have done the swap, you may need to tweek the minimum fan speed in the OS if it starts stalling out on you when going at low speed. Are you comfortable with the Linux command lione via SSH?
Unfortunately, I've not seen anyone chime in with a specific model as a replacement. Once you get one installed, then you'll need to see if it stalls out or needs a spe4ed boost to cool well enough. If it does, then those can be adjusted via SSH.
I waited weeks for the fan to arrive from China, by the time it arrived I was busy and the existing unit had stopped making any noise, so I humbly admit I've let sleeping dogs lie, for the moment.
