What kind of items traders sell is random the very first "trader" (little boy on the beach) could sell a belt with +thiev or if unlucky you don't get one till Amadias Sanctuary.
Keep in mind that some traders (Warfare trader in the cave in Fort Joy) get new equipment every level up you get, so it is pretty likely they will sooner or later have the item you want.
I just always max lucky charm early for that extra chance to find magic items. (Lucky Charm 2 minimum required)
Last edited by Victor_Creed; 04/11/17 11:43 AM.
