Almost all OS now for new computers is Win10. So there's no choice for new computers.
No choice if you're buying a laptop or a name brand desktop anyway.
There are still a few places that build custom computers that will put Windows 7 on a computer for you, but they aren't likely to offer Windows 7 with the latest generation processors. Microsoft has conspired not to support the latest Intel and AMD processors on Windows 7.
Buying a new computer with Windows 7 doesn't ensure an old saved game will work.