Preheat oven to 400°F. Line a large baking sheet with parchment paper.
In a large bowl, whisk together the all-purpose flour, almond flour, sugar, baking powder, and sea salt. In a processor, combine butter and a small amount of flour mixture (~1/4 cup) and process until butter is pea size. Add to the rest of the dry ingredients. Chill.
In a small bowl, whisk one of the eggs with 1 teaspoon of water. Set aside; this will be the egg wash for later.
In a separate bowl, whisk the remaining egg with buttermilk and almond extract until smooth. Form a well in the center of the flour and butter mixture, add the blueberries, and slowly mix in the wet ingredients until mostly incorporated.
Scrape the dough out onto the parchment-lined baking sheet. Using your hands, gently bring the dough together and press into a 9-inch circle. Using a sharp knife, cut the dough into 8 triangles (cut all the way through, but no need to separate).
Brush the tops of the scones with the egg wash and sprinkle with the sliced almonds. Bake until golden brown, approximately 27 – 30 minutes. Let cool 5 minutes. Using a sharp knife, separate the triangles into individual scones.
In a small bowl, whisk together the powdered sugar and lemon juice. Drizzle over the scones; the glaze will harden as it cools.