There is actually... it's part of git and it's called "git svn". I didn't use it when I migrated so I'm not sure if I can backport all of my work retroactively now.
However, I'm not likely to go back to committing to the old subversion repository. Keeping them in sync would be pointless (I migth as well just commit to svn if I'm to do that). One of my reasons for leaving subversion behind was the sheer amount of downtime SoureForge had and then constant painful slowness of the repository.
I belive, but I'm not 100%, that you should be able to, off your own, clone my git repository and then keep it in sync with an svn repository you manage. Something like:
[text]svnadmin create /var/svnroot/swiftmailer git clone git://github.com/swiftmailer/swiftmailer.git swiftmailer-git cd swiftmailer-git git svn init -s file:///var/svnroot/swiftmailer git svn dcommit[/text]
This probably won't work as-is, but something along those lines. Keeping svn and git in sync then becomes a process of doing: