OP: I guess you could start by asking Jewish shopkeepers. There was one or two blocks with a lot of Jewish bakeries and other food shops just east of Pueyrredón, somewhere between Corrientes and Santa Fe (sorry can't narrow it down further, used to walk it lots of times but it's been a while).
Also might consider Abasto and try falling into conversation with other customers at the kosher McD's. But maybe you'd rather be below the yenta network's radar
Also might consider Abasto and try falling into conversation with other customers at the kosher McD's. But maybe you'd rather be below the yenta network's radar