How to legally get High Sierra?

Hey guys.

I believe that my problem is quite uncommon, but I hope that somebody will be able to help me.

As you might have guessed, my goal is to install macOS on my normal computer. I own an old mac-book (first unibody model, non pro version, around 2008), so acquiring the installation program that is needed for the installation would normally not be a problem. However, the macbook is so old, that when I want to download macOS from the appstore, it gives me a warning and says that my computer is too old. Fair enough. There is a program, I forgot what its called, to get the installation file anyways. The program works fine, but the problem is, that it downloads Mojave and not High Sierra. I can't (or rather don't want to) use Mojave, since the nVidia driver still hasn't been released.

So, is there a way to legally get the High Sierra installation file from the AppStore or any official source with my 11 year old macbook?

Any help is appreciated.