Simply sell items to the black market for supply. However if interested in finishing the game I would recommend that you either save and then do this then go back to the save before you sold everything or that you do this late game after you have most things researched. As the game progresses some enemies become extremely rare to encounter or stop spawning altogether. A lot of these enemies parts/corpses are required for research so you could unknowingly set up a huge roadblock for yourself.