If you were careful, the answer to this question is hidden in the picture for this guide. In fact, the game has an operation that you can carry out on any cleared location.
You can produce ammo and explosives in certain areas of the map (I guess where there are repair stations) by going to the strategic map and pressing the O key to open the list of operations (in the same place where you train mercenaries, militias, repair equipment, heal and so Further).