The Argentinian government many years made it law to not allow the promotion of grass fed meat products . For me this is a crime of huge proportions and completely discrimatory . In most western societies grass fed beef is actively promoted at a higher price but as a consumer we must have this right to eat healthy . There are a few places in Buenos Aires that you can buy grass fed beef but its not promoted on the labels . You must ask the server to give this to you . Completely and utterly prohibitive but that is how it is . The numbers below will help you . Make sure that you ask for carne de pastura and they will assist you . Amics in Palermo has very high quality grass fed beef products as does Benjamin Market in Acasuso.
Chivito and Cordero are similar but tastes are a bit different. Usually chivito has very less fat and is softer. I am able to find pretty decent pre-cut "costillas" de Lamb in Jumbo Palermo ( cerviño y bulrich) on Tuesdays and Thursdays. Highly recommended for lamb fans,