@sunvalleylaw - Miranda Ski School in Santiago is a great place, very nice skiing and ambience, in fact I will be there next November for a stop of LAST (Latin American Senior Tour - www.latinwaterski.com)
In the city of Sao Paulo (Guarapiranga Lake) there are 7 slalom courses, great skiing conditions but no coaching available, I can introduce you to some friends that will be happy to ski with you.
In Rio de Janeiro there is one coach available, Greg (whatsApp 55 21 999 610 817), he has a nice ZO ski boat and in the morning the skiing conditions are usually good, the lake Rodrigo de Freitas is in the middle of the city, really beautiful site.
In Belo Horizonte (where I live) no coaching available but I will be glad to ski with you anytime you want, there are 2 lakes with 5 courses about 30min from Belo , both with ZO boats: www.clubeserradamoeda.com.br
There are nice places also close to Buenos Aires, I have been to a few but unfortunately do not have contacts, check their federation site for more info: www.fadew.com.ar