I'm not sure there's any real procedure to get old versions of the full installs. If you happen to have an even older version, you can pick up the maintenance upgrade for 3.2(2c) here:
http://www.cisco.com/cgi-bin/tablebuild.pl/callmgr-archive
Otherwise, you can work with your local Cisco office and they should be able to hook you up. If you absolutely, positively can't get anywhere with them, post your e-mail address here and I will try to help directly.