Had to check my item list to remember, but yeah, there's a warhammer in "Life of the Party." On Angelwatch's second floor, in the southwest corner, is a barracks. The hammer is in a footlocker along the east wall. It's easy to overlook this room, as it's out of the way and there aren't any loot or item pickups to be found.

Incidentally, there was also a warhammer in "The Unwelcome Guest," in a chest in Karras's quarters, but it was replaced by a mace in the final mission.