please support filtering based on whether the package is already in the archive

I'd like to focus my attention on sponsoring new versions of packages that are already in Debian. Would it be possible to offer some filtering based on whether the package already exists in the archive or not?

Originally reported by @lindi at https://alioth.debian.org/tracker/index.php?func=detail&aid=313459&group_id=100127&atid=413115