If you didn't have an active or reliable internet connection during a hard disk install, you probably didn't get the mirrors added at that time. This will cause issues in the future when seeking new or updated software packages from the Kali repos.
To add the sources:
1. Use your favored text editor to open /etc/apt/sources.list
2. Add the following two lines to your source list:
3. Save and you're good to go!
You can check that the sources have been added and are being used by loading Add/Remove Software from the Sys Tools menu and selecting System -> Software Sources.