Green Tripe is an amazing supplement for any dog. It is exactly what you are thinking - the stomach lining of a prey animal. It contain natural enzymes, omega fatty acids and a whole lot of nutrients.
We have personally seen sick dogs get better after their diets were supplemented with raw green tripe.

At BauHound Haus, we carry a beef and lamb tripe in raw form.

We also have dehydrated beef tripe and canned tripe.