Try Kinefot on Talcahuano 244/250
http://www.kinefot.com/

I spent a month in Buenos Aires last year and used Kinefot for processing Ilford XP2 (C41) and HP5, with scanning to CD. (I was paranoid about have xray damage on undeveloped negatives when I flew home so wanted to find a local lab to process the film.) Good quality results and a very reasonable price.

Good luck, and enjoy your stay in this great city.