In a large 8-quart punch bowl, combine tequila, cream of coconut, lime juice, and heavy cream. Stir well to blend until smooth. Add sparkling water just before serving to add a light fizz. Arrange lime slices around the edge of the punch for decoration. Rim the punch bowl and glasses with sugar for a frosty look. Serve with a ladle, pouring into sugared glasses. Garnish each glass with a lime slice for an extra festive touch.