Look for a dietetica, many offer the same brand of organic eggs, but the name of the brand escapes me. They are in a pink carton. Also some shops in Barrio Chino carry them, and my local verduleria carries very yummy eggs which are advertised as being fed "100% alimentacion base vegetal" or "fed 100% vegetable-based feed," which have the best orange color and are yummy yummy.
I think a Dietetica is your best bet, they have them all over the city. If you happen to be in Palermo, my favorite is Mirasoles on Malabia between Charcas and Guemes.
