Try to find food with only one protein source (ex. fish or turkey or chicken or liver or beef), avoiding lamb and rice. The reason to avoid lamb and rice now is so that if later in life you need a mild food for a while you can move to that. You will probably have to resort to getting food at the petstore. I use Science Diet, it is costly, but has been very good for my guys. They also get yogurt but only about once a week.
Plus I give my guys left over mild foods such as plain hamburger or sausage, scrambled eggs, white or brown rice, corn chips with no flavoring, pretzels, Rocco likes orange peels.