I buy it through "Mas cerca es mas justo" which is a non-profit that distributes "fair-trade" goods from local farmers and producers. https://www.mascercaesmasjusto.org.ar/como-comprar
You have to order through a Google Form and pick it up at a designated date & place.
I recommend Punta Chica in San Fernando. I realize it would be considered as a suburb and that might not be your goal but what's nice of it is that it has BAICA close by. It also has great public access to the river (which other areas of BA don't have) and the activities that come along with it...