You Could use a All Grain Pigeon Feed, it a all kinds of grains in it. Most have at least 14% protein and I have seen it all the way to 21% protein.
Also you can get Pigeon feed with or without Corn and most if not all don't have Soy in them.
Popcorn, Whole Milo, Canadian Peas, Whole Wheat, Maple Peas, Austrian Peas, Oat Groats
Canadian Peas, Austrian Peas, Wheat, Oat Groats, Milo, Red Proso Millet, Maple
If you cant get a all grain pigeon feed at you mill you can try -
Cracked corn - 31%, Wheat - 17%, Red Wheat - 16% Yellow/Green peas - 16%, Barley - 7%, White Wheat - 6%, Buck Wheat - 5%, Safflower Seed - 2% ( Above mix should be 12% Protein - 3.1 Fat ) also note that % is by weight, so 17% would be 17 lbs