Fans!

That's 38mm deep. He needs it 25mm or so.

Yeah, reason it needs to be so thin is because it has to fit between the motor and back wheel. 25mm works but I've only got maybe 1-1.5cm clearance to the back wheel, and probably ~1cm to the motor, so even 25mm is kind of pushing it

I got bored and was looking at fans and found a few you might be interested in.

Delta EFB0812LB 80x15mm Low Speed

Delta EFB0812SH 80x25mm Triple Blade High Speed

Sunon 80mm x 25mm Extreme High Speed Fan - 50.6 CFM (KD1208PTBX-6(2)318.AF.GN) - FrozenCPU.com

Delta 80mm x 15mm Fan - Bare Lead (AFB0812LB-F00) - FrozenCPU.com