I did this once. I just offered my free services to someone on Craigslist. I ended up tutoring a young woman from Brazil, which was great for her because I speak fluent Brazilian Portuguese. It makes it a lot easier to explain some concepts if you can just do it in the language that the individual speaks. Anyway, try Craigslist. The top level of the Burger King at Corrientes/Callao is a really good place to meet! Good luck!