Lost one AirPod

Yes. You can replace a lost Airpod with Apple. :) - You will have to purchase this however, as this is not covered by your consumer warranty or Apple Care.

Please see the following link regarding replacing your Airpod, scroll down to the bottom and click the "UK" flag and then select your own country to get it in your region/currency if you are outside of the UK.

AirPods Repair – Official Apple Support

See "Replace a missing AirPod or case" here.

How to find your lost AirPods, AirPods Pro, or AirPods Max - Apple Support