Dude! Bummer.
Went through my brakes earlier this year because I had a leaking piston seal and decided it was time to do the whole system from top to bottom. Seals - master and caliper, pads, rotors, pump out the old fluid...
I was sure I had a couple sets of pads. Absolutely sure.
Started the master cylinders, both sides. Moved on to the pads on the non-leaking side, got that done, undid the other side, went to put my second set of pads that had to be at the bottom of the box because I new I had more. Just knew it.
It only took a week and a half or so to get a second set of brake pads.
But at least, my airplane was in my hangar...