Sorry to hear that you have lost your right earbud.
Regrettably SoundSport Free headphones are not interchangeable as the two headphones are linked. I would suggest if you would like to look into service options available to you is to reach out to your local support team. You can reach out to your local support team via clicking this link and selecting your region, this will redirect you to our website. Please scroll to the bottom of the website and there you will find a 'Contact Us' tab, this will provide you with all the relevant contact information for your country.
I apologize we could not do more to assist.