Spoiler Alert: Once Zukowsky is killed, take out the enemies around you. Then go back in Zukowsky's office and shoot or punch the painting of Zukowsky's face. Unlike any other paintings in the level, it will fall off and where it was there will be a safe. You can't open it, but it's still cool.
Go to the bunker by the bridge. the bunker has a wall near the boxes, take a terralite gl or acog(may work with others) and use a clip shooting at the wall, if u stay there touching the wall shooting for long enough, u wont lose any ammo, if u walk away it stops working (it doesnt work with secondaries).
1. Go back in Zukowsky's office and go to the back of the room. There will be one on a wooden table.
2.When you breach the bathrooms, go to the right side. In one of the bathrooms, a Wolfe is on the floor next to a toilet.
There are probobly more in the level, but I haven't found them yet so I'll keep looking. But be warned, they only have a small amount of ammo even when one is used as ammo for another, so use them wisely.