Go to the online shop and buy Cubase there. Then it will give you an activation code.
Unfortunately, you may not be able to buy a download version. Many updates or upgrades are available as downloads but an original version may only be available in the box (it may come with several DVDs). In that case you will have to wait for the box to arrive because the activation code will be in the box. I think the Elements version can be downloaded immediately but the Artist and full versions come with some content that is not in the trial.
HTH
J.L.