You can obtain an international driver's license in Argentina.

From WikIMAS

The Automovil Club Argentino which issues International driver's licenses requires a DNI among other things (http://www.aca.org.ar/servicios/documentacion/frame.htm) so if you don't yet have your DNI, you would need to obtain your license in your country of citizenship. If you plan to drive around Argentina, there are many police checkpoints and you will be stopped -- if you don't have an International license, the fine is around $500USD. The majority of police will suggest you pay them whatever you're able to, but it's better to avoid the hassle.

In the U.S. you can obtain an International license by mail through AAA: http://www.aaacolorado.com/travel/international_driving_permit.asp. You need two recent signed photos and a copy of your U.S. driver's license. You might also contact your local embassy for assistance in obtaining one.