Here's the "forage" mixes from Stock Seeds:
Forage base deer and turkey mix:
alfalfa, alsike clover, chicory, peas, ladino clover, oats, red clover, timothy, turnips, wheat
Upland Game Bird mix:
annual sunflower, buckwheat, millet, oats, partridgepea, milo, millet
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My book "Feeding Poultry" by G.F. Heuser talks about pasture--it says that frequent mowings are needed to keep the pasture tender and palatable. Recommended components include perennial clovers, alfalfa, perennial rye grasses, meadow grasses, fescue, bluegrass, and timothy.
Any kind of grain may also be used, but is temporary. You can also sprout grains for a yummy treat.
Since a lot of the listed grasses are pretty standard in the mixes that people use for lawns, you could probably just use some fresh grass seed from the hardware store for the bulk of your "pasture." And then supplement with a bit of something else.