Are you looking to install this on or an older machine ?

Some online "gray market" software sites still sell leftover product keys. However, these can be hit-or-miss regarding legitimacy and activation.

Sometimes, buying an older refurbished laptop or desktop is the easiest way to get a machine that already has a legal Windows 7 COA (Certificate of Authenticity) sticker attached. The Risks of Downloading

Since official retail sales have stopped, your options are limited to the secondary market:

While Windows 7 remains a favorite for many due to its simplicity and performance, buying and downloading it today is a bit of a challenge. Because Microsoft officially ended support for the operating system on January 14, 2020, it is no longer sold or distributed through official channels. The Official Status