If you kept the packaging or manual to your airflosser you can go online to their website: USA.Phillips.com
It’s a good idea to register your airflosser on their website as well. You’ll get all kinds of product support their like recall notices, coupons for replacement flossers etc.
Scroll down to product support and click on it. Scroll to accessories and parts, click on Sonicare, click on AIRFLOSSER then scroll down to replacement flosser heads. They are sold in a 2 pack.