If one travels, you might notice it. Each one has a blue orb on their signage or somewhere in the shop. The merchants seem to specialize in foreign goods, but often buy local produce and products, to trade in other places. They seem totally unrelated to the others. It seems to be a secret organization, but nobody knows for sure.
Pcs learn of high power magics that allow them to banish weapons and suits of armor to some 'elsewhere' place until such time as they need it. reduces encumberances, gets fewer questions, and when the PCs get jumped by thieves in the ally, they can summon their suits of full plate armor with weapons drawn.
Lesser powers would allow them to summon their weapons from another physical place, drawing them to their hands like Luke skywalker summoning his lightsaber on Hoth.