My daughter went to GRU last year on my NW miles (we got the ticket right before the miles required went up!!!) - her college friend is from there. She went CO. I found that the available seats were few and far between. Basically we had to check EWR-GRU and IAH-GRU daily until we found something then find anything Mycity-IAH as it turned out. Called NW and had them put the available legs together. Biggest thing I learned is that the High volume travel days in Brazil are not necessarily the same as ours- what I thought was our low season was actually their high travel season. Complicated by the fact that CO has only one flight daily from IAH and one daily from EWR

Anyhow, she loved it, hope you do to. Sorry I can't help you beyond GRU.