apt-get install giving 404

If you're getting a 404, it means that the file in question is not on the server. This probably means that your local package list is out of date. Update it with

apt-get update
apt-get install subversion

To see what versions of a package are available for installation on your system, do

apt-cache policy subversion

It'll tell you which versions of subversion are available for installation. It will also tell you which version would be installed if you don't explicitly ask for a specific version.

When an Ubuntu release becomes unsupported, it is moved to old-releases.ubuntu.com. If you change the host for all your gutsy-related repositories from <whatever>.ubuntu.com to old-releases.ubuntu.com and then perform an apt-get update; apt-get install subversion it should all work nicely.