I can highly recommend Pilar at Argentina Escapes. I worked for a high-end travel company here in Buenos Aires a while back and we always used them for booking flights and services. You can contact her on +54 11 4322 4141. I think most (if not all) of the people in the office are bilingual so you won't have any problems communicating and they are efficient and reliable. www.argentinaescapes.com

Suerte!