The two sides of the headphones and the charging case are all pre-set with the information needed for one-touch connection to and from each other. This setting can only be configured at the Service Center with all three components present. For this reason, you can't simply replace one missing part.
If you lose the charging case or one side of the headphones, send the remaining items to the Service Center so that a replacement for the missing part can be acquired and reset with the remaining components. Go to Product Repair.