Search the following locations to find the corresponding Reflex Injector.
Mission 2 "Awakening": After the elevator cinematic, you will find a double door that requires a key card. Go past it and enter a small room to find the keycard on a dead man. Return to the first set of doors to get into the room with the Reflex Injector, which can be found on a shelf.
Mission 3 "Discovery": After going through a vent, there will be a worker executed by a flamethrower soldier. Look on the floor of the bathroom in this room to find the Reflex Injector.
Mission 4 "Withdrawal": Immediately after Intel 26, go down the stairs to the left. The Reflex Injector is on a counter. Once you reach the elevator that goes up you will see it.
Mission 5 "Replica": *After looking at the abomination with the monitors, go through the double doors directly across from it. Turn off the valve to a flaming pipe that blocks the room with the Reflex Injector sitting on a shelf before coming into the abomination monitor room.
Mission 6 "Ruin": During the battle around the downed plane, once upstairs, go all the way to the back of this same building. You will find a box with both Intel and a Reflex Injector on it.
Mission 7 "Top": *The Intel and Reflex Injector are both on the same table when you arrive at the closed doors that you have to open. When you exit the power armor, it is to the left, up some stairs, and in the room on the table.
Mission 8 "Elementary": It is hidden under a projector in a room in the hallway with yellow lockers and where ghost starts to appear. It is the room on the right after the trophy case.
Mission 9 "Nurse's Office": After seeing two soldiers get incinerated, look in the bathroom on the right in the hallway, where there are some corpses over a barricade.
Mission 10 "Snake Fist": After returning power and stopping the lockdown, go back to where Intel 54 was found. Go down the ladder where the mechanical arm is moving. It will uncover the Reflex Injector for you to pick up.
Mission 11 "Keegan": When you walk upstairs, go to your right and back down the stairs. You will find the Reflex Injector and armor seen earlier.
Mission 12 "Epicenter": Just before you enter the theatre, enter the room where the laser man breaks out the doors. The Reflex Injector is to the right on a counter.
Mission 13 "Approach": Look in a little nook away from the major part of the same room as Intel 70. You can reach it by going up the platform, going straight off it, turning to the right, and dropping down a ladder and climbing up another one. It overlooks where you initially came in the room.
Mission 14 "Climax": Immediately as you exit the tunnel after seeing "the tree", the Reflex Injector is directly in front of you.