If you are heading to Buenos Aires and looking for the Graffiti Scene, I highly recommend to contact the guided tours of Graffiti Mundo.
Graffiti Mundo is a non profit organization that promotes the local Art scene and the artists.
The tour guides have a great knowledge and well familiar with the artists as well. There are various tours and workshops as well.
You might be surprised, but the majority of the Graffiti scene in Buenos Aires is legal and moreover, some home owners invite the Artists to paint the building facade.
The tour lasts approx 3 hours in various streets mostly in Palermo and ends in a bar which is dedicated to Street Art exhibits.