I would like a late season bloomer. It would have to be disease resistant
There are no disease resistant mango trees guaranteed to not get a disease.
Are you concerned about bacteria, viral, fungal, or another organism causing this disease?
Why do you think the Keys would be more prone for this organism to attack your mango trees in the Keys vs. elsewhere in South Florida?
I grow Keitt as my late season mango in Palm City, Fl and often have mangos through the end of October.