This is a random weapon mission in Piety.
The weapons store in the back of the Haymaker's sports store usually has ammo left around in the counter. However, recent reports suggest there is one store out there that's been untouched.
The mission requires you to go to a Haymaker's sports store and collect the weapons from there, the sports themed zombies that spawn here can make the sporting goods store slightly dangerous, but you can easily run past them and loot the gun shop at the back easily. Inside the few containers you can find some ammo for rifles and pistols as well as at the back of the counter some shotguns and rifles.
The couple of containers in the small shop have inside some ammo, moslty .38 win/9mm/.458 win. The rifle rack at the back usually has pump shotguns left there as well as a Model 70 Safari.
No exact loot chances for the containers are here yet.