There is a Mariachi group in Santiago from what I understand. There is a Mexican Restaurant in Los Jardines that you can get contact information from.
I don't know the name but from the intersection of La 27 with La Ponce Pou Saleta(La Metropolitano) turn right at the fourth roadon the right, C11, and it will be on the left at the end of the road where it intersects with the road that goes around the park.