This may shed some light…
Anyone looking for an older copy need to receive (and the seller MUST provide) either a dongle containing the license or an unused Activation Code. The latter not really easy to verify for the buyer.
Any Cubase Full license allows to run any previous Cubase Full versions down to SX. Previous VST/VST Score versions used a different system and are not included. As a Steinberg Cubase X user, one can ask Support to receive previous versions’ ISO images. Minor versions work otherwise, as the Artist/Elements, Studio / Essential and SL/SE are considered to belong to different product “ranges”.
As Steve and jaslan wrote, it is the license that matters, and is the one you pay for. So absolutely check it is provided, as disks/boxes/manuals without a license are worthless.
In the mean time, if no takers on your request here (as I can’t help you with that) I’d keep asking Steinberg Support about getting a Cubase 5 ISO image…and you may want to stop gushing about your previous cracked version while asking 
I have no idea if it’s a specific problem importing cracked Cubase 5 projects into legitimate Cubase 8, assuming they use the same kind of .cpr project file. Unless someone chimes in to confirm that - I doubt many would want to admit they know - you may just have to find out when you get your legit Cubase 5 ISO image installed.
Good luck!