I’m not nopick but I’ll answer anyway 
. The always on fan is 5V. The part used by LulzBot is (pick the 5V one): https://www.lulzbot.com/store/parts/40mm-pelonis-low-flow-fan
From the manufacturer: c4010l05bplb1-7 3.87cfm
Same size from the same manufacturer: c4010m05bplb1-7 4.82cfm
Or the big guy (40x40x20): c4020h05bplb1-7 8.21cfm
Personally, I like Noctua fans: nf-a4x10-5v (4.82cfm) or nf-a4x20-5v (5.53cfm) and they are available on Amazon: 40x40x10 or 40x40x20
While I was on Amazon I found this one, https://www.amazon.com/4010-5V-Brushless-Cooling-Fan/dp/B071KSNNQ5 5.5cfm but I have no idea about its quality (but the price is right).