I'd contact the Paulista Go Center
https://www.facebook.com/paulistagocentertheir email appears to be nihonkiinbrasil at hotmail dot com
It's not the one founded by Iwamoto Kaoru, but it is in São Paulo, exists since 2012 and seems well established. I am sure, one of them knows somebody who knows somebody..
Good luck with your research!
EDIT: Here is a claim, that São Paulo Go center was founded in 1989:
http://www.inaf-go.org/iwamoto/The homepage of the São Paulo go center seems defunct. I couldn't even access archived versions through the way back machine.