They honestly drop in a lot of places, it's just they're hard coded to spawn more often in areas that were pre-war military checkpoints.

I had a pretty lucky drop in hardware town, where in 2 ammo boxes there were 4 fusion cores each.

Well, already finished the game, and a week after that I realized I could ask my companion to enter a power armor.
Didn't use them a lot but now that I found a full x-01 one I can sleep well, just need to complete the rest of the sets and find a way to display them nicely.

Finally got the chance to upgrade to a PS4.
Fallout 4 is the first game I got. So far enjoying it.