They are found within An Unburied Relic. They give updates at random, most were rusted and useless. They are not trackable.
All 4 are found in the area between ( -228, 7, 368 ) Copy/waypoint -228, 7, 368 - ( -480, 84, 230 ) Copy/waypoint -480, 84, 230 down to ( -154, -82, 111 ) Copy/waypoint -154, -82, 111