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 1.4 branch. This branch is the code for the stable release (1.4.x).
svn co svn://scribus.info/Scribus/branches/Version14xor for those with closed SVN ports on their firewalls:svn co http://scribus.info/svn/Scribus/branches/Version14x
Scribus 1.5svn – Development. This branch is the code for the experimental version (1.5svn). This code may be highly unstable or may not even work or compile at all!
svn co svn://scribus.info/Scribus/trunkor, once again, for those with closed SVN ports on their firewalls:svn co http://scribus.info/svn/Scribus/trunk
From here, continue with the Compiling and Installing using CMake instructions.