1. In a blender, combine tequila, curaçao, coconut milk, and lime juice. Cover and turn to high speed, then gradually add raspberries, blueberries, and ice. Whirl until margarita mixture is smooth and slushy.
2. Put sugar and lavender blossoms in a small bowl. Rub with your fingers or mash with a spoon to release some of the lavender flavor. Rub glass rims with lime wedge to moisten. Dip rims in lavender sugar, coating evenly.
3. Pour margaritas into sugar-rimmed glasses. Garnish with lavender sprigs.