Although I am not a mojito drinker, I have been with others who partake -- and have had no trouble finding them...Many (most) of the resort lounges have a full bar -- and would happily make a mojito for you. I say most because some are confined to the specialty drink menu you find on the table. Also any restaurant with a lounge has full bar...so you will have no trouble finding mojitos.
Also, most of the TS restaurants at Downtown have a full bar (Fulton's, Portabello, Wolfgang on Westside etc.). I'm guessing mojitos are available there too.