Here is a link to the seeds/grains Excello Commodities offers:
Pigeon Blends, Wild Bird Mixes, Nuts, Safflower, Sunflower, Dried Fruits and Vegetables, Soak mixes and more This is where I buy my mixes. You won't want every seed that is listed, but it'll give you a good idea of what's out there. Then just google the seed you're thinking of including to see what it's composed of.