Need to fallback to 3.5.13.0. Package archives?

I did a successful install of 3.5.13 on one of my Ubuntu Lucid systems back in August. I had a problem with the X system not autodetecting my monitor properly, but circumvented that by forcing it to the right configuration with a manually-reated xorg.conf. Yesterday, I made the mistake of doing an "apt-get upgrade" on that system that upgraded trinity to what appears to be 3.5.13.1. Now that system is de-GUIed: if I start KDM, the X server refuses to start. There are no errors in the log: it just gives up. This looks similar to the problem I had back in August, but may be different. I tried installing XDM. That fixes the X server startup, but the system fails to create the desktop: I get no taskbar, and the system continuously spawns konqueror instances that immediately crash. The packages I installed 2 months ago have disappeared from the repository. The links to the install CDs are broken. A google search for the package filenames returns no results. Is there an archive or mirror someplace that hasn't been purged? Or am I just totally screwed? Thanks, Ran