They do actually have some surprisingly big robes available, as if anticipating that very tall people arriving are a possibility, but whether this particular band happens to have those available can be up to you. If his particular escort doesn't have the big sizes in stock, they would at least have one that fits, albeit somewhat awkwardly. Worst come to worse they will give him a second robe to make due with. If they don't have the big robe initially they may swap him out for a more suitable one later once the groups converge, depending on whether or not he's fostered negative relationships with the soldiers.