I know that there is an exchange at the Vanguard Quartermaster for the old Year One materials, but it's been quite a while since that system was introduced, and I'm pretty sure that, like me, many players have exhausted their armor materials. Since Banshee sells Weapon Parts, and the Factions take Armor Materials as donations, I think that one of the vendors should sell the Armor Materials. Since the Vanguard Quartermaster exchanges them anyway, thats the best option.