There is an unlisted subcommand to apt-cache called “madison”. This will simply list all available versions:
$ apt-cache madison git git | 1:2.11.0-2~ppa0~ubuntu14.04.1 | http://ppa.launchpad.net/git-core/ppa/ubuntu/ trusty/main amd64 Packages git | 1:1.9.1-1ubuntu0.3 | http://us.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages git | 1:1.9.1-1ubuntu0.3 | http://security.ubuntu.com/ubuntu/ trusty-security/main amd64 Packages git | 1:1.9.1-1 | http://us.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages git | 1:1.9.1-1 | http://us.archive.ubuntu.com/ubuntu/ trusty/main Sources git | 1:1.9.1-1ubuntu0.3 | http://us.archive.ubuntu.com/ubuntu/ trusty-updates/main Sources git | 1:1.9.1-1ubuntu0.3 | http://security.ubuntu.com/ubuntu/ trusty-security/main Sources
In all likelihood this will work under Debian, too.