Sonar Theme originally used by default in OpenSUSE, and here are GTK2/GTK3 Sonar theme designed by half-left.
The theme comes with the metacity theme and the GTK2 version. License and authors are in the theme directory. Note that the metacity theme and GTK2 theme are not my work, just distributed via GPL.
Recently the theme has been updated and now it has many improvements for GTK2 and GTK3 as well.
Unzip and copy sonar folder to this path
Check the theme description for more information and the updated changelog in the deviantart link.
Also check the related posts down below for more half-left work.