Here there are some themes for your GNUstep Apps. Mainly these themes are for people that use desktops like Gnome, KDE, XFCE,... Just untar the package and copy it on ~/GNUstep/Library/Themes at your home directory. You can set the theme with SystemPreferences.app.
GNUstep SVN Themes
GnomeTheme is a plugin to make a GNUstep theme based on the active Gnome theme. Is under development.
WinUXTheme is the theme for Windows. You can active this on installation or with SystemPreferences.app.
You find more at GAP.