There is a mod claiming that a majority of armors are tagged under MP as opposed to SP so they are not available in SP. My brother installed it and started a new campaign and he had armors in the shop we had never seen before. So hope that answers your question.
**Mod no longer necessary. Problem fixed with 1.0.4 patch** Currently there are 200+ armors that have the tag >multiplayer_item='true' making them unavailable for use in singleplayer. This file w
www.nexusmods.com
"Currently there are 200+ armors that have the tag >multiplayer_item="true" making them unavailable for use in singleplayer. This file will add them back into singleplayer."
Modders beat the devs to the punch on this one. Love to see it, Hopefully the official fix shows up in tomorrow's patch.