Put the frozen cherries, crushed ice, mint leaves, lime juice, rum, and simple syrup in a blender. Blend until smooth.
Pour the mixture into chilled glasses and top with crushed ice. Garnish with lime wedges and cherries.
In a small saucepan, over medium heat, combine the sugar, water, and lime zest. Bring to a boil, then reduce the heat and simmer for 5 minutes, stirring occasionally, until the sugar has dissolved. Remove the pan from the heat and allow the syrup to cool for 20 minutes. Strain before using.