Following on from my Bangalore restaurant post, I searched in Mercadolibre and found a small almacen known as The Beer Emporium who sell a very nice range of British and other European beers. In fact, I'd already been to Caballito once today in order to collect some PC spare parts, so after lunch I zoomed back and bought a couple of tins of Old Speckled Hen, one of my favourites as it happens.
Here's where they are if anyone is interested:
https://www.google.com.ar/maps/place/Beer+Emporium/@-34.6158309,-58.453247,17z/data=!3m1!4b1!4m5!3m4!1s0x95bcca178e888ab5:0x3144b53b5e2ec0b0!8m2!3d-34.6158309!4d-58.4510583