revert to previous version

I installed an update of Thematic to our wordpress installation, but it has messed up the child theme and our website no longer functions properly.

Unfortunately, I didn’t properly back up before updating, so I can’t restore from the backup directly.

Is it possible to get a download of a previous version of Thematic that I can install?

(I would like to fix it so it works with the current version, but right now I just need to get the site working and reverting to a previous version is the quickest way.)