I discovered this site a few months back. https://www.key1024.com
The site is definitly ugly and look like a scam, but for just 32 EUR and protected by Paypal, I wasn’t taking much a risk to try. And it worked perfectly. Keys are completly legit. I used to hack windows on all my computers, and when I realised I could get keys for that cheap, I decided to legalize all my windows.
You pay and got the key by email a few horus later… Once one of the key they send me didn’t work, I emailed a screen copy of the error, and got a new key with no questions asked a few hours later.
And if you wonder, all my windows 8.1 obtained throught this site updated for free to windows 10 also with no problem.
Arnaud