Weapons storage warehouse in Los Santos
Go to the Ocean Docks area in Los Santos. Look for railroad tracks and follow them south until they lead to a building with boxcars. The complex can only be entered by jumping the wall, going through the boxcar warehouse, or by an opening to the right of the warehouse. The boxcar warehouse has a sawed-off shotgun (you will need a car to get it) in one of the cars, a plank bridge that leads to body armor, and gas grenades located at the back exit. A short distance away from the back exit, you will see an entrance to another warehouse. This one is full of crates. Go through the crates to find stairs. Behind the stairs is an AK-47. Go up the stairs to find more body armor.