I just toss grit on the ground in the run with the scratch grains once in a while.
Feeder:
https://www.backyardchickens.com/articles/aarts-waste-free-funnel-bucket-feeder.67218/
OS holder:
Feeder:
https://www.backyardchickens.com/articles/aarts-waste-free-funnel-bucket-feeder.67218/
OS holder: