The latest source code can be downloaded from sourceforge via anonymous cvs. The CVSROOT environment will need to be set as follows (for Linux using bash):
$ export CVSROOT=:pserver:firstname.lastname@example.org:/cvsroot/sqlunit $ cvs -z3 checkout sqlunit
Alternatively, you can download the latest released tarball (which also contains the source, but may not be the latest) from the download section. If you are going to be doing any development work for SQLUnit, however, I would recommend getting the source from CVS.
Note that tarballs prior to version 1.4 cotained only the SQLUnit JAR file due to a packaging bug, and are hence binary only. Additionally, you would have to go to CVS to pick up the DTD file. Thanks to Arjen Stolk for pointing this out.