Try
Casa Zanzi on Talcuhano and Corrientes.
I can't say for sure that they have good stuff, but if they don't, short of taking your chances on Mercado Libre, I don't know if anyone would.
Just kind of stumbled upon this thread last night, after a google search to look for some action here. I've been here three years, and I'm glad to see so many people in the city.