If you like vintage there's a couple of stores in Flores, Av. Rivadavia 7700-7900. One is more "window shopper" friendly, the other is like a huge warehouse, if looking for something special or not readily available on sight, ask the attendants and they will usher you to one of the upstairs floors where thousands of chairs, tables, objects, furniture await their new destination.
http://www.larueda.com/es/index.html (it will be open next Monday & Tuesday -carnival holiday) - Rivadavia 7901
http://www.casamontepio.com.ar/ - Rivadavia 7701