There is a scientist named Crockett in one of the rooms in the Hubologists' San Francisco base (who, incidentally, is not an adherent of Hubology) that can harden power armor. He can upgrade it for a fee of $10,000 (which can be immediately stolen back) or can be threatened into doing it with a high Speech skill. Alternatively, you can negotiate to have fuel transferred from the Steel Palace to the USS Quetzel in exchange for his services. The process takes 1 day. However, he can only harden two sets of power armor.
If having killed the AHS-9, it is not possible to get the needed dialogue for the hardening process but it's still possible to receive the armor already given to him.