You can get a tarball of the most recent release of Scribus from Sourceforge: http://sourceforge.net/projects/scribus/files/.
Thanks to Anduin.net there is also an anonymous SVN repository, which is updated hourly. Use of this code is only recommended for those who want to stay on the bleeding edge. Instructions for getting the latest source code via SVN:
Scribus 1.6 branch. This branch is the code for the stable release (1.6.x).
Scribus 1.7svn – Development. This branch is the code for the experimental version (1.7svn). This code may be highly unstable or may not even work or compile at all!
From here, continue with the Compiling and Installing using CMake instructions.