The installation can be done with the help of a PPA, but a source package is available
Nitrux OS Icons, a pack of handcrafted icons that are compatible with a lot of operating systems, including Ubuntu 13.04, has been updated to version 3.1.4.The icons in Nitrux OS are infinitely scalable, which means that they are compatible with a large number of operating systems and there's no quality loss.
With over 6,000 icons available, it's hard to find a program that doesn't get its own personalized icon. According to the developer, the action icons have been removed from NITRUX-Buttons, and couple of action icons have been revised.
Also, more missing Gnome Shell icons have been corrected, Gnome Weather is now using the correct icon, and various symbolic icons for Gnome 3.10, Gaupol, gImageReader, Gnash SWF Reader, gPDFText ebook editor, gscan2pdf, and ImageShack Uploader have been implemented.
The installation for Ubuntu 13.04 is quite simple and can be done from a terminal:
sudo add-apt-repository ppa:upubuntu-com/nitrux
sudo apt-get update
sudo apt-get install nitruxos
You can also download Nitrux OS Icons 3.1.4 right now from Softpedia.