Natural bran is bran that has had nothing added to it.

yes. Bran Cereals, 5-10 grams - All-Bran, Bran Buds, 100% Bran, Raisin Bran

Not normally. Bran flakes are usually made from wheat bran and wheat flour to bind the bran into a flake.

Bran Vargas goes by Bran, Brandolf, and Dolf.

Unprocessed bran is not the same as oat bran; it would be referring to wheat bran. Have you checked at a health food store? They will definitely carry it. As far as subbing the oat bran, it would depend on the recipe.