I went to a food market in Mar del Plata and I found a stand of an organic farm in Chapadmalal, near Mar del Plata, called Granja La Piedra.
The lady behind counter said they sell their products in at least 3 places in Buenos Aires, but she was not able to name any because she was hired for that event, only.
They sold goat yogurt and a number of goat cheeses (ricotta, ricotta salata, gouda, etc.), plus marmalades.
The yogurt was excellent, and we chose to have it with blackberry jam as in a dessert.
For those visiting Mar del Plata, they can visit the granja and have lunch there. Details on http://granjalapiedra.com.ar/ and on their FB page.
The market I visited is at Museo del Mar, daily 18 to 23 in summer. There were other interesting stands of fiambres, quesos, dulce de leche Chimbote, ice cream made with liquid nitrogen, etc. Overall, about 20 stands, but only 3-4 worth mentioning.