Hello! I have experienced the same. I also tend to develop these white spots and I agree that they seem to appear less and less often if I increase the raw percentage in my diet.
Me too I was much too skinny on raw food. I am looking into the mostly raw omnivore approach and I have added some soft boiled eggs, kefir and butter to gain some weight.
I don't know if this may help you, but I have noticed that grains make me feel bad in many ways so I am having only oats (which make me feel great). I think that these white spots are likely to be the sign of malabsorption of some nutrient, and since grains contain a lot of antinutrients it could be related. After all no one gets to eat many grains on the raw food diet and this could explain the improvement-.
I do not have the other symptoms you describe, but besides brittle and white-spotted nails I have extremely dry skin esp, on hands, thin and fragile hair, and all of these suggest malabsorption of some mineral.
It could be true that we are lacking Ca and Zn, after all the fact that supplements did not help you could also be explained by some food you are currently eating that blocks their absorption no matter how much you get of them. Try to cut out grains for 2 weeks and see what happens.