is it possible to buy an AirPod pro case alone?

Yes. See the following from How to find your lost AirPods, AirPods Pro, or AirPods Max - 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 AirPods pricing and service options.

You can buy a replacement case but I don't know of a way to track a case.