Check with pet stores who deal with indoor birds. Many of them will sell oyster shell in bulk, and it's fine as long as the pieces are large enough.
Mary
Are you sure that it's a bird eating those eggs?
Sometimes you can see egg yolk on the beaks or faces of your egg eaters, definitely helpful. Are the egg shells thick enough, or do you have someone laying very thin shelled, breakable eggs?
Are all your birds eating the egg shell? Is the...