There is one way and I know this by heart: if you go down a road near Novac then find vault 34 try your best and survive killing all of the ghouls.

After that find flooded stairs and go underwater. Then look for a drowned ghoul and search him, he should have a passcode. Then look for another one and loot him for another.

After this look for a computer and start the pump station. Then go to the nolonger flooded stairs and clear it out. There should he another computer. Activate what you can do then look for the Overseer's office.

You may need dynamite because there will be a turret, then kill the Overseer, loot a passcode and type it into the computer behind the turret. A pop up should appear saying <open armory door>, go to the armory then clear it out. After that take what you can.

There should also be a rare carbon named the All American and finally your rare prize - the riot shotgun!