Into a large bowl, measure the teff (or buckwheat) flour, whole wheat flour, coconut, brown sugar, baking powder, baking soda, salt, and cardamom. Blend the ingredients well with a fork.
Add the cubes of butter to the bowl and toss to coat with the flour mixture. Use your fingers or a pastry cutter to break the butter into the flour until it is in tiny, pea-size pieces evenly distributed into the flour mixture (sort of like coarse, wet sand).
Drizzle the buttermilk over the dough and gently stir with a fork just until the ingredients are mixed. Don't over mix or the scones will be tough. Add the dates and walnuts and stir just until combined.
Spread a little flour over a cutting board and invert the scone dough on top. Gently pat the dough together into a round so it is about 8 inches in diameter. Use a large knife to cut it into 10 triangles. Transfer to the 2 baking sheets using a spatula.
Bake until the scones are deeply browned and cooked through, about 22 minutes.