There are shops that are all along the Rastro (in Madrid). They are open during the week and some on the weekend. They may or may not have what you are looking for. I would have my doubts about the farm equipment. Possibly books, and maps.They will have household antiquis, furniture and art work. I would check with Spanish customs before making purchases of these items, as some countries have laws prohibiting the export of historical items.

Have fun and stay safe.