According to this How to install software or upgrade from an old unsupported release? question, EOL releases are archived to http://old-releases.ubuntu.com.
But currently, I cannot see Ubuntu 12.10 and Ubuntu 13.04 to be available on this website, while all others(since 4.10) are available, as you can see in the screenshot below
So has canonical and/or Ubuntu devel-teams decided not to archive EOL releases any more? or is it work to be done?
They don't transfer EOL immediately to http://old-releases.ubuntu.com, they keep them on http://releases.ubuntu.com or sometimes http://cdimage.ubuntu.com/releases/ for a while. The cdimage one seems to get cleared faster. I don't know how this time period is determined or it's length it's just something I've noticed when downloading isos.
Ubuntu 12.10 Page = http://releases.ubuntu.com/quantal/
Ubuntu 13.04 Page = http://releases.ubuntu.com/raring/
Remember their are also 3rd party mirrors sometimes available that may have older isos still available such as http://mirrors.nl.eu.kernel.org/ubuntu-releases/ which still has 12.10 here: http://mirrors.nl.eu.kernel.org/ubuntu-releases/12.10/
Quantal has now appeared in the old-releases.ubuntu.com mirror! Happy Days :)
[obsolete answer follows] This week the main ubuntu mirror seemed to drop 12.10/quantal repository package pool altogether. Old-releases still has not picked it up, and like everyone else here, I'm struggling to find any information on future plans to do so (or not).
In the meantime, we found a repository that still contains some packages: http://ftp.belnet.be/ubuntu.com/
Currently we can only confirm the quantal and quantal-updates distributions, with main, and universe sections for each, restricted and multiverse are there but fairly incomplete.
While this does not answer the question I thought I'd document my resolution while there is still some life in at least one repository:
Mirror the repo locally
Here's an example of doing it with debmirror - I'm behind a corporate firewall that only allows http/s (no rsync or ftp), and requires authentication so I've accounted for those restrictions in my options. You'll need about 87GB for binary packages for i386 and amd64 architectures combined (from memory, sync still in progress here). I would triple that if you need source packages too:
Hope that helps -