I experienced some similar issues with my first few sets of English orpingtons I was growing out. I switched from a standard chick starter to a broiler starter with higher protein. That seemed to help with the leg issues I'd been having. It also helps them feather out.
Purina person and TSC recommended Flock Raiser. I really liked Purina's Free Range product, as it has soldier fly larvae mixed into the pellets, but apparently it's also a layer formula.... and since I have a cockerel...
Anyway, our TSC is the only place I can get stuff without driving over an hour... and they don't have a grand selection to begin with... but they do have Flock Raiser (or All Flock, I don't remember) Will that suffice for protein and lower calcium? I have oyster shell grit out all the time.