I lost the AirPod case. Can I purchase just the case?
I just bought new Airpods and unfortunately misplaced the case while on a trip. Can I purchase just the case?
Yes. See the following from If your AirPods are lost - Apple Support
If you still can't find your AirPod or Charging Case, or if something is damaged, get the serial number and then contact Apple Support for a replacement. Then learn how to set up your replacement.
You can also learn more about AirPod pricing and service options.