For syrup, in a medium saucepan combine the 2 cups water, the honey, and lavender buds. Bring to boiling over medium heat; immediately remove from heat. Let steep 10 minutes. Pour syrup through a fine mesh sieve into a 2-qt. pitcher; discard lavender buds. Let cool to room temperature; stir in lemon juice. Cover and chill 4 to 24 hours.
To serve, combine the vodka, 2 cups sparkling water, and the chilled syrup. Pour lemonade over ice cubes in tall glasses. If desired, serve with lemon wedges and lavender sprigs.