If you haven't already found those font files, or for anyone else who has run into this problem, you should be able to find the files in your C:\Windows\WinSxS folder. Open that folder in File Explorer and the type calibri in the search box at the top right. It should find all of the original calibri*.ttf files from your Windows 8 installation. You can drag them from there into the Fonts folder.
On my system, the Office 2013 installer also deleted the Constantia font files. If that happened to you, then after reinstalling your Calibri files, enter constan in that search box and you will find the constan*.ttf files which you can also drag into your Fonts folder.
This is a serious bug in the Office 2013 installer. It should not be deleting existing fonts!