You can get the most recent version of Scribus from:
There is also thanks to Anduin.net, anonymous CVS access is updated daily. Only recommended for those who want to stay on the bleeding edge. Scribus 1.2.x is now deprecated. Instructions for getting the latest source via svn:
Scribus 1.3.3.x - Stable
From here, continue with the Compiling and Installing using autotools instructions.
Scribus 1.3.5 target branch. This branch is the code that will end up as 1.3.5, and eventually 1.4.0.
Scribus 1.5.0svn - Development
CMake is required for any version after 1.3.4, as autotools support has been removed.
From here, continue with the Compiling and Installing using CMake instructions.