Animal foods are the only natural source of vitamin B12, but many products, including soy products and cereals, are fortified with B12 so it is widely available in the food supply. Other good natural sources include shellfish, such as clams, mussels and crab, fin fish and beef.ome of the best sources of vitamin B6 are poultry, seafood, bananas, leafy green vegetables such as spinach, potatoes and fortified cereals. Your diet should include 1.3 milligrams of B-6 daily to support new red blood cell growth.