you can use the wiki here, to look for other clothes, what NPC sell them.
But they just sell other lv 1 armors i think. Possibly lv 16 armors, since wep sellers have lv 1 and 16 weps.
otherwise get into crafting and make the armors, that's what's intended i guess, since there's no armor sellers selling all armors or such.
i think only gridania has boots for example, so you must go there to buy boots, and pants in ul-dah etc :)
some leves will randomly give clothes too.