I lost one of my AirPods how do I get a new one

You can buy a replacement for your lost Airpod from Apple.

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

AirPods and AirPods Case Replacement - Official Apple Support

AirPods Pro$ 89 each

AirPods$ 69 each