Boiler Room: An Arrow rifle can be found bottom middle on the boiler.
Broken Home: A Revenant gun is located on the middle bridge.
Cathedral: A Revenant gun and grenades are at the bottom middle of the map.
Cave In: Check around the platforms in the middle of the map to find an Arrow rifle.
PSI Topside: There are sniper rifles hidden around the map.
Shaft: Battle to the bottom of the map to obtain a Arrow rifle.
Shaman: Look around the center totem, there may be something hidden in the tall grass.
Town Hall: The bridge below the roof gap has a Revenant gun.