I lost my left airpod can I buy it?
I want to buy just the left airpod
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.