Part 1- The Semi-Auto Pistol is the first weapon you will find parts for in Rise of the Tomb Raider. You’ll obtain the very first piece right after you fight the huge bear in the Siberian Wilderness. It’s in the strongbox right before moving on to the next area.
Part 2- You’ll find this part at the beginning of the Soviet Installation. It is located in a small building in the area right before you reach the Train Yard base camp.