Tie mint in a cheesecloth bag, and place in a saucepan. Add sugar and water; bring mixture to a boil. Cook, stirring constantly, until sugar dissolves.
Remove from heat; cover and let cool. Remove and discard cheesecloth bag. Refrigerate mint syrup until ready to serve.
Scoop melons with 1-inch melon baller or ice cream scoop, and place three pieces on each serving plate. Serve with berries, and top with sorbet and fresh mint leaves. Drizzle with mint syrup.