Hello, You might try ebay. You may have to buy a broken Nest Hello used just to get the puck.
This is just a user forum so maybe someone will have one to sell you.
You can also try reaching out to Google Tech support and see if they can help. To do that you need to open an official support ticket. Here is the link. If they get you going please return here and let us know how it went.
https://support.google.com/googlenest/gethelp
