The note can be found at the ammo dump, on top of a broken terminal in the trailer.
Frank, you're not gonna believe this. There's a working suit of POWER ARMOR in the Monongah plant! It's out of juice, but if I can get my hands on a fusion core, I'll walk it back here myself.
I think Joanne mentioned she picked up a core somewhere. I just need to come up with a convincing reason why we need it. Can't let anyone know about that armor until it's in our loving care.