Spinich is good for them, and is very nutritious. Grass is also good! Mine LOVE grape leaves from our grapevines, hopefully some others can chime in with more suggestions.
Wait, so none of your chickens are laying yet? I wouldn't offer oyster shell until the day I got my first egg. At least that is what I have been told numerous times on BYC. The oyster shell is to strengthen the egg shells, but if they are not laying, why offer it?
Also, please do not think just...