1. Preheat oven to 400°.
2. Weigh or lightly spoon flours into dry measuring cups; level with a knife. Combine flours, granulated sugar, and next 4 ingredients (through salt) in a medium bowl; stir with a whisk. Cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal.
3. Combine 1/2 cup buttermilk and egg; stir with a whisk. Add to flour mixture; stir just until moist. Fold in blueberries (do not overmix dough).
4. Turn dough out onto a work surface lightly dusted with white rice flour. Pat dough into an 8-inch circle on a baking sheet lined with parchment paper; cut dough into 10 wedges, cutting into but not through dough.
5. Bake at 400° for 18 minutes or until edges are golden and center is firm. Remove scones from baking sheet to a wire rack; cool on rack 10 minutes.
6. Combine powdered sugar, lemon rind, and 1 tablespoon buttermilk in a small bowl, stirring with a whisk until smooth. Drizzle glaze over scones; let stand 5 minutes. Serve warm.