Grate zest from one lime; toss with sugar and spread in thin layer on small plate. Set aside. Cut remaining lime into wedges; reserve 2 wedges for garnish.
Place remaining lime wedges, six blackberries and mint leaves in cocktail shaker. Using a muddler or wooden spoon, press mixture firmly to release natural juices.
Pour Allen’s cranberry cocktail into shaker; top shaker with lid and shake well for 45 seconds.
Run lime wedge around rim of 2 tall glasses. Rim each glass in reserved lime-sugar mixture. Divide ice evenly between glasses. Strain juice mixture over ice; top with sparkling water. Thread remaining blackberries onto two cocktail picks.
Garnish spritzers with blackberries and lime wedges.
Tip: Make these spritzers for adults by adding 2 oz gin and 1 oz triple sec to the cocktail shaker along with the juice if desired.