Tethers Unlimited is working on ways to build antennas larger than could be flow up on a rocket in GEO, I'm sure they're pay for refined metal once that gets going. Any location with humans in space would probably like to buy some loose gravel just for greater radiation/impact shielding, especially for anything outside the Van Allen belt. Space is currently a $300 billion industry and I wouldn't be surprised if you could sell $1 billion worth of raw materials. It's getting an asteroid to Earth for that cheap that's the really hard part.