I actually found some which where described as new and ordered them. Will need to look into the pinout then whenever the switches arrive.They look interesting, I certainly haven't seen anything like those when I was looking for fans about 1/2 year ago. You'd need to do soldering anyway, because the ones inside the switch have the standard 4 pin connectors and not the small one like these.
Also, the fact they're used is a bit concerning. Fans tend to develop additional noise over time. The question is, do you want to give them a shot...
That's interesting, because, when I was experimenting, I had a larger PWM fan that I tried plugging into the board and it wouldn't spin. Then I noticed that the coloured wires order of the native fans didn't match the schematics available on the Internet and, indeed, it was different, which I verified using a voltmeter. Maybe they have different fans with different pinouts in different production batches of these switches...My SX6012 (original mellanox) powers my 4 pin noctua fans just fine. Still been meaning to build a shroud/air duct to use larger (and much quieter fans), I don't use it rackmount or all that often.
Turns out those have an amperage of 0.075 vs 0.81 so it seems I fried them when connecting them :/