You can find liquor stores in Little Havana off Flagler street. The area is just West of Bayside. Duty free is only available if you are flying in from outside the country. Otherwise, as Zoomer said, you can buy on the ship providing you are not counting on it to use while at sea.
Mike,
Spirit Jan 18th,
Pride12-02
Elation12-01
Triumph12-00
Sensation10-99
Inspiration12-98
Sovereign of the Seas12-97
Scandinavian Sky04-82.