Here is a script that I use to fetch the latest revision of a svn project. The trick lies in finding that revision number. It isn't the Revision of the repository but the Last Changed Rev. The rest is straightforward git svn.
#!/bin/sh
SVN_URL=$1
GIT_DIR=$2
REV=`svn info $SVN_URL | awk -F': ' '/Last Changed Rev/ { print $2 }'`
mkdir -p $GIT_DIR
cd $GIT_DIR
git svn init --stdlayout $SVN_URL
git svn fetch -r $REV:HEAD