You were given a full set early in the quest line. The person who gave you it also sells those same items.
BTW, I don't recall any of the quests needing the armor (although I was using it all at the time)... where are you stuck ?
the person who gave me the armor the first time requires that i give her a piece of the armor to upgrade for me to continue the quest line, and i sold the armor a looong time ago