Are You Using a Legal Copy of Windows? - Business Owner Stories
The short answer is:
One of the most reliable ways to get a legal license is to buy a refurbished "Business Class" laptop (like a Lenovo ThinkPad or Dell Latitude) that still has the Certificate of Authenticity (COA) sticker with a valid 25-digit product key attached. Red Flags: What to Avoid buy original windows 7
Since you can't buy it from the source, your options are limited to the secondary market. Are You Using a Legal Copy of Windows
Here is the reality of the market today and how you can safely navigate it. The Official Status Here is the reality of the market today
The internet is full of "discount" keys for $5. While these often activate, they are frequently "gray market" keys—meant for educational institutions or large corporations—and can be deactivated by Microsoft at any time without warning.
While Windows 7 can still be installed and activated today, remember that it no longer receives security patches. If you do set up a "new" Windows 7 machine, it is highly recommended to keep it offline or use it strictly for offline tasks to avoid modern security vulnerabilities.