Malted rice is called kome-koji and is used in making sake. It's not really "malted" but rather infected with the mold Aspergillus oryzae which turns starch to sugar. You can buy kome-koji and mix it with other rice to make more kome-koji, or you can buy koji-kin, which is just the mold itself.
Also, why can't you eat those grains? Do you need gluten free beer