Edit: (I tried to cut out the flub on this, sorry was too long) To summarize, I mean give players a means of getting materials they are short on by giving up materials they have an excess of. Not a shop outright, I agree that wouldn’t fit GZ, but something.
My one thought is a system like the constantly rotating assignments, but focused on collecting a random material and giving a random material in return. I constantly have 1000+ explosive, steel, lead, adhesive, but rarely have more than 100-200 of anything else, such as thread and textile. Even if the exchanges are asymmetrical, i.e. give 200 and get 50-100 I’d still find this a valuable mechanic.