I found an install download of Cubase VST/32 5.1r1 on the net. I don’t recall the site where I found it but I got there by using Google. Mind you, the download has a couple of files included that are deemed to be illegal. However, if you just ignore these files the installer will install a completely legal copy of Cubase.
It worked with my USB e-licenser, where the corresponding license is stored, on a Win8.1-64bit machine. It might have helped that the copy-protection files were already installed thanks to Cubase 8 residing on this computer.