A few days ago I gave you a tip about how you can obtain Windows 8.1 downloadable media just by supplying your product key. This is a great option in the event you actually need the media for one reason or another.
You can also do the same with Microsoft Office 2013/365 if all you have is a product key card obtained through purchase from a retail outlet and/or preinstalled on a new PC.
Here's the site: https://officesetup.getmicrosoftkey.com/
Just enter the 25 character product key and choose the installation.
Obviously, if you already have a subscription to Office 365, you can just use the normal method for installation inside your Office account at http://office.microsoft.com/, but this gives retail buyers a good option for obtaining media.