Digging some of your own dirt is good - they're already used to anything in it. Add some sand, maybe a touch of DE, if you're so inclined. The key ingredient, though seems to be wood ash. You can make your own simply by burnng clean wood in a fire pit or grill. Make sure you use regular firewood (branch trimmings are fine,) nothng pressure treated and no chemicals (like starter fluid.) While you're at it, do some hot dogs or s'mores or whatever floats your boat ... Why should the chickens get all the benefits, right?For nest bedding? Sounds comfy! As long as theirs no chemicals, I don't see why not.
But for dust bathing, just go dig up some dirt that you know won't have chemicals in it, my chickens prefer my neighbor's dirt, which is an issue!