OK, there are a ton of music stores in a small area. I can't remember for sure, but I think that it is Peron & Uruguay maybe. There is DEFINITELY a "district" and I think that Peron is the street with lots of shops on it (if not, then it is Sarmiento... one more towards Corrientes from Peron). And I think that Uruguay (
WRONG) is the other cross street
CORRECTION: Talcuhuano (This intersection has music stores on 3 or 4 of the corners.) but they would be in that Talcuhuano to Callao area. (
SEE BELOW FOR UPDATE)
I've popped into a guitar shop on Borges right near Plaza Italia to check on used Classical Guitars. It was either Gurruchaga, Borges, or Thames, but it was absolutely just doors away from Plaza Italia (Sante Fe) on the Belgrano side of the street (meaning on the side closer to Juan B. Justo/Belgrano).
There is a Guitarria place on Cordoba right after it splits and the other side becomes Estado de Israel (~3600 Cordoba) where a guy makes classical and/or steel string guitars by hand. This will run you OVER US$1,000, but it's cool to check out and I'm sure he would be helpful if you happened by his shop. (He's on the left side just a few to 7 doors after the gas station as you are traveling away from town on Cordoba.)
There is a place on Corrientes & ~Uruguay where you can take guitar lessons and I would think that that is a music store and/or they would know where to find used stuff.
There's Mercado Libre
http://listado.mercadolibre.com.ar/guitarras/
And finally, some of the music stores sell low end stuff. Whether it is a music & "discos virgen" music place on Sante Fe near Talcuhuano to a
MUSIMUNDO at several of their locations, you can find brand new
crapo brands. (I have noticed that there is a "TEXAS" brand that I've never heard of in the States buy that I've seen in a few store fronts.
So that's enough for the two or three of you to start with and then report back so that the others can decide what they want to do.
You're welcome.