the game depends on the level of the player when the cell is loaded to determine what type is spawned. some cells are a 100% chance to spawn a full suit of armor, whilst others only spawn with a few parts. your luck stat may also be a factor in deciding what armor and how many pieces the game spawns for you. if you want x-01, dont bother looking until your past level 28. also try not to enter indoor cells (buildings, ie 35 court) until you are a certain level to make sure you get the armor you want.
also dont bother looking for t-60, just cap a brotherhood knight or follow him until he is killed after he jumps down from the vertibird and take his armor. you can remove the paint.