Part 1 - The first spawn is left of the entrance into the Central Filing. The second spawn is leant against the filing cabinets in the middle of the room. The final spawn is in the middle of the two windows in that room next to the exit.
Part 2 - The first spawn is in the War Room under the left staircase. The second spawn is on the other side of the mystery box on the lower level of that room. The final spawn is at the end of a computer station leading to a zombie window.
Part 3 - In the South Laboratories left of the power on small boxes. The second spawn is behind a crate next to a door next to a teleporter. The final spawn is in the North Laboratories near a teleporter next to a zombie window
Craft - You can build the shield in either the Weapon Testing room or in the Central Filing.