However, I see that many brazilian aiports are missing the METARs - This is because only the main or international airports are on the NOAA - or any other international database.

Most Brazilian airports have their METARs thru the local REDEMET database (the oficial Brazilian authority) - They have their APIs available, and I think it would be easy to add these METARs to Windy as well - I would be glad to help if needed.