im looking for that too

you can find it by a room but you need to go to a place in front of the door and find a
serverd arm

i have arm..won't open door..

Turn around and head through the mutant-infested fire-strewn ruins and pick up some med
kits (as needed) and the severed arm of the security guard (press X to interact with the
environment, which hopefully you've figured out by now). Use the arm on the left pad, then
quickly (before the arm falls off the pad) run over and hit the other one with your own
hand.

Instead of getting that maddening failure message, this somewhat gross method will unlock
the door and give you:

A tough mutant that's chewing on a soldier inside the armory.
Ammo and med packs—it's the armory, remember?
The LR1 security card.
Grab it and head back to Crispy so he can unlock the hangar doors.