went through this with our silkies. Despite doing the usual plenty of calcium in diet, wooden eggs, etc. It came down to a behavioural approach... they learned that something 'yummy' came (at least sometimes) from pecking something "egg shaped", so that's what they'd do, no matter how much good food was already out for them (even when that included left over scrambled eggs from breakfast!).
What I did was get those plastic easter eggs that break in half to put candy in. And inside, I put a small rag soaked with vinegar. Replaced "broken" plastic eggs every day. After a few days of pecking all the eggs they wanted, and getting nothing but vinegar, they never pecked another egg again! Even years later, when I got a particularly stupid hen who laid eggs while roosting, they wouldn't go near the broken egg under her perch.