Upgrade Cubase 5 to 10 without Cubase 5 installed

So Windows 7 on my trusty studio machine nuked. The maker of my machine can provide me the original Windows 7 image to return it to factory condition, I just have to re-install Cubase 5. Problem is, I do not have my Cubase install DVD anymore. I do have my dongle with my registration key, obviously. I couldn’t find anywhere on Steinberg site where I can download Cubase 5 anymore. And I don’t mind paying to upgrade to 10 here, but it would certainly be nicer to save almost 300 bucks on the upgrade vs buying Cubase 10 outright.

So my question is, what are my options here if I can’t find my Cubase 5 dvd? If I buy the Cubase 10 upgrade, is having my Cubase 5 dongle enough, or is not having the software on the machine a non-starter for the Cubase 10 upgrade installer?

I am probably going to buy a new machine later this year running a customized version of Windows 10 Pro, and run the latest and greatest Cubase 10x but I kinda just need to get back up an running right now.

My interfaces are a pair of Steinberg 816s over firewire, so I’m pretty much all-in on Cubase no matter what.