Rimlock keep/staple (Mousehold NR3)

We've just re-hung my daughter's kitchen door after several years in storage and discovered that the keep for the lock is nowhere to be found, so if anyone has an old one lying around, we could offer it a loving home. Not a common term for many, so picture attached. It's not the lock body, it's the separate bit on the left! Probably about 3" / 75-80mm long