Can I Find X-01 Parts in Fallout 4?

The south Boston military checkpoint has a full set of leveled power armor. If your level is high enough(above 26) it'll be x-01.

From http://fallout.wikia.com/wiki/X-01_power_armor#Locations :

• A helmet can be found at Proctor Teagan's shop on The Prydwen behind a door locked with a Master level terminal, and can be stolen.
• If the player character is a high enough level when starting the Brotherhood of Steel quest "Blind Betrayal", a full set of X-01 missing the helmet can be seen being worn by Paladin Danse after completing the quest.

Bought from:

• Various pieces can be purchased from Rowdy at Atom Cats garage, depending on player character's level. Rowdy's shop refreshes at the same time as shops in the settlements.

X-01 armor appears to start spawning at level 26.

There's a location called the Abandoned Shack in the Glowing Sea that has a few armor pieces on a frame.

The shack is actually an entrance to a military bunker. Fight your way down through the complex (or jump down) and there's a frame with about three pieces of power armor on a frame tucked in the corner. To get out of the building, you can either climb up again or reboot the maintenance mainframe from a terminal in the corner (which activates the elevator).