Either turkey or pheasant feed is suitable if they are kept in a run. You should be able to get it from any agricultural feed store. They also appreciate any greens. They will even eat nettles. As a treat they adore mealworms.
Mine are free range as they were hatched here so don't go far, just wander round my garden, and the neighbours'. They therefore find their own insects and greens and are quite happy with wild bird seed or wheat.