Please note I am no longer support this plugin. Use at your own risk.
Ever wanted to duplicate a theme quickly and easily from the safety and security of your WordPress Admin? Look no further! With Duplicate Theme you can… duplicate a theme! All while in your WordPress Admin. Choose the theme to copy, provide a name and voila! Have all the joy of the original theme, but in a new theme! No more messing around with FTP and online File Editors to duplicate themes. Why waste time downloading, uploading and editing style.css? Just install this plugin and BAM! you can duplicate a theme!
You can download it here: WordPress.org – Duplicate Theme