Top Motor 80x25mm Case Fan, Sleeve Bearing, Low RPM, 4pin.
12V, .11A, 1.32W, 2200RPM, 28CFM, 24dBA, Sleeve bearing 20k hour MTBF, 18in leads w/ 4pin molex power connector, RPM signal output, includes mounting screws.
SX830 comes with 2 of them, and there's room for 3 more. I'd suggest you take ball-bearing types.