If you sided with Tenpenny during the Tenpenny Tower quest, there is still a way to obtain his suit non-violently. Wait until he has started sleeping, then reverse pickpocket any clothing with a damage resistance greater than two into his inventory. Exit the interior map cell, and return to find him wearing it. The Lone Wanderer may then pickpocket Tenpenny's suit from him (this only works if the clothing given to him is in good condition and has a better armor rating than his own).
If Tenpenny is killed by the ghouls as part of the Tenpenny Tower quest, he will be stripped of his clothing, making the suit unobtainable.