I like to use bluebonnet game conditioner on my layers, as it has pellets already (and tons of grains for a hardy gizzard) but I also mix in some more pellets either feather fixer or layer depending on the time of year, also roosters can have layer feed I've read a lot of people giving it as a whole feed to their flocks.
Im starting my own mixes of feed though after this bag of conditioner and feather feed is gone! Been reading about lots of good things chickens could eat but never see them in feeds! So I get to make a unique blend
Oyster shell and grit should be readily available anytime during a chickens life, however as chickens it needs to be crumbled! Happy Squaking!