If you want this perk ASAP, you can do this in the prologue. After you come down the elevator and kill the two soldiers, there are 5 helmets in this room. Reload your checkpoint. From where you spawn, there are 2 helmets in the room to the right. Then go through the room with all the guns to find two more helmets on the shelf at floor level in the next room. Then turn left and you'll see the Skyrim helmet. This one does NOT count as far as I could tell, but there is another helmet on the desk directly behind the one with the Skyrim helmet. That's 5 helmets. Reload your checkpoint 20 times and you can get this before you ever even start your first firefight!