The kind of places where you would most be able to sell these goods (planar metropoli, like Sigil and the city of brass) also tend to be the kind of places where both A:adventurers want to go to stock up anyway and B: word can travel pretty fast. And the kind of tricks that lead you to be able to do this also tend to give you the ability to access said places with ease (if you went the level 1 wish method, you can bring yourself anywhere once per day).