Because official retail sales have ceased, you are limited to the secondary market:
: You can sometimes find cheap, older computers at garage sales or on Craigslist that still have a Windows 7 Certificate of Authenticity (COA) sticker with a valid key attached. Critical Risks and Considerations Is it safe to buy windows keys off 3rd party sites? buy windows 7 professional 64 bit product key online
: Sites like Keysfan claim to sell discounted legal keys by purchasing them in bulk from Microsoft. Because official retail sales have ceased, you are
: Sellers on sites like eBay or Amazon often list "New Old Stock" (unused physical boxes) or OEM (Original Equipment Manufacturer) keys. Because official retail sales have ceased