I’m also travelling with Carnival soon and received an email with the following information below. As they are advising guests of the need to wear masks, I don’t believe there will be free masks onboard as the cost would be enormous, but I could be wrong.
“All guests will be required to wear masks in all indoor spaces (except when eating or drinking and in their stateroom), outdoors when in large congregate events where physical distancing cannot be maintained, during the entire embarkation and debarkation process, on buses and water shuttles (where applicable) and while indoors on any shore excursion. KN95 masks are more protective and are highly recommended for wearing.”