Very few plants are that high in protein. Insects would take massive quantities although some do raise a lot of mealworms. Collecting wild ones would be very time consuming. Fish meal is often used as supplemental animal protein for chickens. I haven't seen any around here though. Soybean meal is usually not too difficult to get your hands on. Both may have to be mixed with water or something moist though since a lot of chickens will ignore fine powder left behind in the feeder. Cat and dog food is also sometimes used and I would grind some up for my button quail since I couldn't get higher than 22% protein feed here but you have to watch the salt content.