I pre-ordered Bioshock Infinite from GameStop, and forgot about entering the code to get the Comstock China Broom shotgun. I'm wondering how you obtain this weapon. Does it appear in the vending machines, or do you pick it up from the environment?
The "China Broom" Shotgun is the standard shotgun in the game, and there's nothing special you have to do to find it. You'll find enemies carrying throughout the game.
The GameStop preorder bonus is a special skin and "damage enhancement" for this weapon, which has stars down the side of the barrel. Whenever Booker picks up a shotgun, it should get these unique benefits.