Collectable can be found on the upper wall of the side room in the maintenance room between the Green and Blue zones.

Collectable can be found in the maintenance area between the Green and Red Zones. It is found behind debris and barrels and can be shot by standing on the ramp.

Collectable #3 can be found in the cafeteria on top of the grill.

#4 can be found behind a flower pot in the Reception area.

#5 can be found in the bar section adjacent to the lounge. It is attached to the fridge behind the bar.

#6 can be found in the Auditorium by standing on the stage and looking into the projector room window above the seats. It is located on the light in that room.

#7 is found in the elevator room next to the first testing room. It is sitting on top of the a barrel.

#8 is in the research room, placed inside of a crate that requires a jump in order to be able to shoot it.

#9 is located next to the east stairs of the second Testing room.

#10 is located in the maintenance area between the blue and yellow zones. It is hiding amongst the pipes

#11 Is located at the top of the stairs in the maintenance area between the Yellow and Central Zones behind some Barrels.

#11 is located in the maintenance area between the Central Zones and the Red zone. It is hidden behind a chainlink fence atop a barrel.

#13 is located in the Square Sub Bay Section in the South-East corner. Its hiding in some boxes. This one is sort of hard to reach and shoot, unless I missed the obvious angle. I had to use a grenade to get it so if you can, avoid this one unless you find an easier angle (let me know if you do).
You can see the boxes it's in from this angle
It is in this top box here. Here is where I was throwing a grenade to get it to trigger

#14 is in the longer Sub Bay behind a drain grate to the south.

#15 is hiding on top of a desk in a room adjacent to the upper floor of Excavation. You can get an angle on it by standing next to the trading pod.

#16 is in the lower section of Excavation hiding in the vehicle.

#17 is in the maintenance staircase connecting the lower Excavation to the Central Zones. It is behind a slightly ajar door.

Using the vehicle as a reference:

#18 is in the Generator Room next to the truck. It is inside an upturned storage bin.
To get a better view of it so you can see it, jump at the window next to the generator room. You can get a shot off from here, but it's much easier to line up a shot from the gap in the door once you know where it is.

#19 is in the stairway that connects to the maintenance between the Yellow Zone and the Central Zones. It is sitting on a shelving unit.
Using the Generator Room as reference:

#20 is in the upstairs room in the Dorms on top of a table in an adjacent closed room. You can shoot it in between the crack of the door. (Thanks Vic=HKC=)
You can see it standing at this sideways vending machine