You can obtain this quite early in the West Office where you find your desk with a dial lock puzzle.
When facing your desk there is a room to your left a few steps in front of you. Be careful as the officer in the room will attack you. After taking care of him there is a safe which you can unlock using the following code.
Go left with your thumb stick until you are on the number 9.
Go right on your thumb stick until you are on 15.
Go left on your thumb stick until you are on 7.
The safe will open and an inventory pouch will be yours and achievement unlocked.