Each Part has a three different locations every time you play. Most of them are in the same area.
First Part: Base.
First Location: Department Store second level next to Jug. Its in the chair.
Second Location: Between Department Store and Operation Bunker. Once you come out on the jug area, you will be in a small open space lead you to Operation Bunker door. Just go straight to your left and you will see a truck and your part is just right there.
Third Location: If your part is not on the second location. Open the Operation Bunkers then, Turn left. On that side there is a shelving next to a computers. Its on the second layer.
Second Part: Visor.
First Location: Armory Second Level. Its between Mystery Box and Catwalk that lead you to Supply Depot Area.
Second Location: Armory Lower Level. Go straight down and the part is just next to a Wonderfizz
Third Location: Armory Third Level. Look on the corner where you will see a box leaning on the wall and your part is on that.
Third Part: Body.
First Location: Infirmary Second Level. Next to a Stamina-Up and its on the top of a broken concrete.
Second Location: Infirmary Lower Level. Look on the floor where you will see a small boxes with bottles inside. Your part is in between those.
Third Location: Infirmary First Level. Part is on the double Deck bed first layer. This double deck bed is almost in the dark corner next to a stair lead you to second level.