Good question. I've never had to buy one. Expendables were always supplied by my employer. Another company that makes the same style of cutter is:
https://www.steinertechnologies.com/
Another type that is reasonable price wise and works quite well on aluminum are these.
https://www.yardstore.com/drilling-a...everse-cutters
HS steel not carbide like the Flipcuts.
If you're ever in Wichita swing by the Yardstore. Used Tooling, Air tools, measuring, bits, cutters from Cessna,Beech,Bombardier,Boeing all end up there Cheap! Pennys VS $. They have quite a bit on their website used as well but prices are at least 2X higher on the site on used items.
https://www.yardstore.com/surplus
I wouldn't buy a used Pancake or Angle drill there though. Those need to be inspected for head wear personally. (wandering drill bits) Unless they note the heads are new.