It isn't here: https://www.microsoft.com/store/productId/9WZDNCRDR64J and link from here https://1password.com/browsers/ doesn't work either.
Seems it used to be there, but now it just returns "We are sorry, the page you requested cannot be found."
1Password Version: 7.0.540
Extension Version: N/A
OS Version: Windows 10
Sync Type: Not Provided