Pescaderia Mellino brings fish fresh from Mar del Plata and they even have their own fishing boats, their prices are reasonable and everything is super fresh. I do not buy fish from supermarkets, except for Jumbo Palermo. The rest is a disgrace. San Antonio and Regente and Ostramar are three good places, but most fish is imported or frozen. Tuesdays and Wednesdays at Barrio Chino when it is fresh.
This being said, you can get very good lamb from some butcher stores, and rabbit.
My oldest son is vegan: carbs + legumes make good vegetable protein, that is a must!