branches in BA located here (phone before going to make sure they have it there. Be sure to specify you want it there, as they may tell you over the phone they have it, and then they tell you they have to order it when you get there!) http://www.kel-ediciones.com/html/locales/default.asp
I work for a company that teaches standardized test prep, USA Tutors International. If you are interested in GRE prep classes, they offer both long-term classes for people residing in Buenos Aires and short-term intensive programs for travelers. They have a great group of highly trained and fun tutors providing a quality service...with an affordable price tag You can find more info on their website or inbox me. Good luck!