You can always anonymously obtain the newest version of KeePassX source code tree using subversion. However, note that a SVN tree is a development version which is often unstable and might not even work properly. The advantage, though, is that you get newest updates und do not have to wait for the official releases.
To access the repository you need to have subversion installed. SVN works on many modern operating systems and can be obtained from http://subversion.tigris.org. If you are using a GUI SVN client, configure it appropriately.
Once subversion is installed you can access the repository. Change, in console, into the directory you want the source code to be saved in. Of cource, a new directory can also be created.
You can download by entering the following command:
svn co https://keepassx.svn.sourceforge.net/svnroot/keepassx/trunk keepassx
The source code will be downloaded into the chosen directory.
To update the source code just enter the following command. Note that you have to be in the appropriate directory.
More information about SVN can be found in SourceForge.net: Subversion (Version Control for Source Code) HowTo.