This is absolutely unacceptable, Galen Keep on stirring it, and mention police and theft and sueing - I don't know about you but this seems to me to be more than just carelessness.
Someone has probably made a nice pair of drop earrings with the two missing ones - it is suspicious that it is two, not one! A nice little earner!
If they farm out their stringing, as they probably do, they have a criminal on their books. That is their responsibility, and it is up to them to do their best to find them and return them to you, and to make sure that the perpetrator receives retribution. Matching them as best they may be the all they can do, but don't settle for that unless there is no other way.
Do NOT let it go. That would be colluding with the lowlife who has misappropriated them.