They can be found in the Hopeville missile silo bunker.
Hopeville Silo - 2nd level security code
Inside an Easy locked desk on the bottom level inside the silo with the rocket, behind some ruined stairs. It removes the lock on the security control level two terminal, one level up.
Hopeville Silo - 1st level security code
The other is inside a Hard locked desk in the Operations room on the second level. It removes the lock on the base commander's terminal in Martin Retslaf's office, top level.