I do have the minigun. If you find the Specialist in Bunker Alfa, you can do missions for him to unlock special guns and special “floppy disks” (to find more loot on the map). First, you have to activate the bunker security and go through the floors again. When you kill the zombies they will drop things such as notebooks, flash drives, and dog tags. Collect as many as you can and return to the specialist to trade the items for guns. If you downloaded a hack for the game where you can split, this task is 100x easier to complete and get the minigun in under 10 minutes.
Finding the motion sensors are a little trickier. They are in turrets in Bunker Alfa once you destroy them, but they are rare. Turrets are not in the game yet, therefore you would not be able to craft one for your base.
Hope this helps!