Begin the level at Rally Point Bravo. Once you get to the first flight of stairs leading to the final area, turn immediately to your left and go toward the small building. Walk along the left side of the building until the gray material stops; turn right and melee the wall. A supply drop box containing four DMR's and one Shotgun should pop out of the wall and land on the ground. If this doesn't happen then it may have already come out on its own and disappeared due to a loading point.