Looking at the Brazilian startup challenge sponsors, there are a few that can help you as well:
http://www.anjosdobrasil.net/
Brazilian angel investors, and
http://startups.ig.com.br/
That's a source about Brazilian startups, maybe they can direct you to a mentor.
Edit: 500 startups did a Brazil round as well, so there's an Y Combinator alternative for you.
Edit2: where do you live? If you live in the south, and there really aren't any startup hotspots (which I find hard to believe), you can always come to Montevideo :) there's a decent startup scene over here.
I know there are tech hubs in Porto Alegre and São Paulo and Rio.
If you're in the north, well yes, that's a bit tougher and I can't advise you much :) the internet is your best bet I guess.