Usually, most of the biggest supermarkets in Barcelona (like Bonpreu, Mercadona, Lidl etc.) use to sell beer at irresistible prices but they don't have refrigerators for keeping it cold (that is one of the reasons why they could keep prices as low as possible).
My trick: when you have a big shopping list, first thing to do when you enter one such a location is to grab one or two six-packs of beers and put them in the ice cream refrigerator (or frozen meat refrigerator), closer to refrigerator's walls, if possible). Than do you shopping as usual. In maximum 20 minutes you will have a bunch of cold-as-ice beers, ready to drink!
Enjoy!