You can find Win 7 ISO files from official sources or reputable websites.
I'm having trouble accessing it from the Windows page, and I'm not relying on the initial Google results.
Download the Windows 7 software from the official Microsoft website.
The sidebar includes connections to the ISOs page https://www.reddit.com/r/microsoftsoftwareswap/
Join Microsoft Live Chat, provide your ISO and they'll send you a link. That's how I did it.
On the platform, a frehs install is typically required to activate the key. You can enter the key after the systems have been set up.
You can also obtain it here:
Latest updates available through early 2017.