Place sixteen 4-ounce ramekins on a rimmed baking sheet.
Split vanilla bean lengthwise with the tip of a sharp knife. Holding the pod open, scrape seeds from each half using the flat side of your knife.
Fill a large pot halfway with water and bring to a simmer over medium heat.
Combine vanilla pods, scraped beans, heavy cream, and 1 cup sugar in a large bowl that will fit snugly into the pot; whisk thoroughly to mix. Place bowl over simmering water; whisk until cream mixture is just warm and sugar is dissolved, about 5 minutes.
Remove bowl from heat and strain cream mixture using a fine-mesh strainer. Pour out hot water.
Sprinkle gelatin over 1/2 cup water in a small bowl and stir quickly with a large toothpick until granules are separated. Pour gelatin into cream mixture and whisk thoroughly. Let sit until slightly cool, about 20 minutes.
Whisk buttermilk thoroughly into cream mixture; pour into ramekins. Cover with plastic wrap and chill until set, at least 6 hours and preferably overnight.
Place blueberries in a large saucepan over medium heat; cook until slightly toasted and starting to release their juices, about 5 minutes. Stir in orange juice and 1 cup sugar. Bring to a simmer and cook until mixture is reduced by half, about 10 minutes. Remove from heat and let cool until thickened and syrupy, about 30 minutes.
Run a thin knife around the edges of each ramekin. Invert panna cotta onto serving plates. Serve topped with blueberry topping.