One major factor to consider when selling stuff, aside from what it's used for, is how hard it would be to get it back if you decide you later need it.
Therefore, I think that the display you get when you right click on an item in the sell menu (which currently just shows an item's uses, and which is usually used to see if an item is safe to sell) should also list if the item can be purchased or constructed.
As currently, ones you haven't discovered yet should be starred out, of course. This would be useful both to avoid spoiling new players and for everyone to remind themselves if the option to buy / construct a particular item has been unlocked yet in their game.
