Dice have been canceled in many ways over the years. Cancellation methods and tools can change with every new Casino Manager at a property. Dice are normally canceled in the casino managers office in small properties. At the Fiesta he had a small punch and did every die himself. If the punch broke he would just buy another one and not necessarily the same kind.
Its possible large casinos send them out but I doubt it. Too many real bad scenarios that could happen.

I am not sure what you are calling rejects, are in fact rejects. Manufactures would have a hard time explaining rejects getting out to the public.

Casino managers are very paranoid about their dice.
I will ask how we do it, but I am guessing our table games Director does NOT let used dice out of his sight until they are canceled.