Some good suggestions all around.

In my area (northern Maine), ideal grouse cover is thick with alders. The preffered food sources are usually clover and beechnuts, alder buds, and of course wild berries.In the southern part of the state, they often inhabit grown-over farmland which holds apple trees, blueberries and other wildberries.

Planting clover, apple trees, chokecherries, etc. seems to me like a good start. Access to gravel is also a plus as stated before.

You didn' t mention what type of cover is available to them already. Partridge like to head for thick cedar swamps or spruce/fir thickets when winter approaches. It wouldn' t hurt to have a few thick evergreen stands on the property.