If you download the Microsoft windows 10 ISO, you should still be able to install it on Windows 8 or 8 pro machines that have the serial number built onto the motherboard
That is what we are told anyways for recovery reasons or replacing the hard drives in windows 8 machines
The iso is free and you can copy it onto a bootable USB stick
FWIW You can also just directly download a USB version directly to a regular USB stick and it will make it bootable and ready to go.