Free range them or put them in a good secure pasture setting. They will find what they need in 'nature'. (Unless you are like us and everything is brown and dead, and even the grasshoppers are skin & bones)
Where I live I have a very high mineral content including Calcium in the soil. The only thing that I am low on is Iron. I fertlize my front yard with an iron blend and throw the trimmings into the garden. My hens get what they need because I let them out every day and add to my yard what the soil is short on. Do a soil test and take care of your soil and the rest will fall into place as long as the hens have acces to feed in the yard that is.
For the first time in my life I wish I had Grasshoppers in my garden. I have never seen one since we moved into our new home. But the hens get plenty of greens and slugs. Another note concerning minerals. I know that some people put the egg shells in the blender and feed them back to the chicknes. I feed the egg shells to my red worm bins and feed the hens worms from the red worm bins.