I've given him a truly decent set of non-PA armor (improved Combat Armor mostly) as well as an improved blend of T-45E and T-51E. The trouble is, in our last foray his PA parts were shot to heck and gone, with several pieces reduced to zero. I can remove the damaged pieces -- ALL of the actually -- but I'm seriously short on Steel at the moment, so I can repair them. Meanwhile, Garvey stands there in the naked exoskeleton and refuses to don the non-PA armor (except for the helmet). In the dialog interaction, there is no way to tell him to exit the suit.

You should be able to talk to him, hit up-arrow for Talk, and then the bottom-arrow option should be Exit Power Armor. If another topic of conversation shows up, you may have to talk it out with him before you can access that option.

First you need to go to Trinity Tower. Then you must make your way up to the apex of said tower. Upon achieving the apex of said tower you shall then be given reason to doubt your ever having read anything by Shakespeare. Once enlightened to your previous folly you shall meet a lovely green hued gargantuan named Strong; who seeks the fabled "milk of human kindness". Accept this mutant of a man as your companion as he is Strong and he can carry more than silly humans. Upon assuring his questionable loyalty you then make way, post haste, back to that son-of-a.....Garvey standing all too proud in your hard earned power armor and point - then simply whisper to the lovely green hued mass of muscle towering over you; "Strong, my son...therein awaits the milk of human kindness...I beseech thee to squeeze it out of that tin can."

Garvey knows what he is...but knows not what he is about to be.

Or you could just do what MarkDb said.

Aw, but what you said was so, so, elegant. Why, it was almost Shakespearean in it's elegance!

And, yes, I will follow MarkDB's advice. Thank you, both.