While you cannot buy it from Google, several "Works with Google Cardboard" certified partners and retailers still offer the viewers:
Google stopped selling viewers directly on the Google Store in March 2021 . Because the design is open-source, you can still purchase official-spec viewers from third-party manufacturers or find remaining stock on secondary marketplaces. 🛒 Where to Buy google cardboard official buy
Since Google open-sourced the platform, they provide the for free. If you have a pizza box and some basic supplies, you can make one yourself: While you cannot buy it from Google, several