You have flyers then. You can get them at your local feed store like Theisen's which is where I get mine:
https://www.theisens.com/products/purina-flock-block25-lb
This is probably a better brand:
https://www.kalmbachfeeds.com/collections/blocks-tubs/products/all-natural-poultry-block
I've used these as well when they were young:
https://www.mannapro.com/poultry/treats/chick-stick
Though if they burn through these that could get expensive, also they're considered treats so you'll want to make sure they're not just focusing entirely on them since they're not a replacement for feed, but supplemental at best.
I generally have these available all winter, along side feed in my garage. In the spring if I have any block left I throw it outside where they range and they'll eventually finish it off or nature will.
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Also to divert them from digging holes to dust bathe in your yard you could put down a tub of sand and they'll love it, I'd probably go with washed river sand, playsand works, but has silica you don't want to breathe if they're kicking it up.
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