Currently, there is not way for admins to search for unpublished content within the manage content area. This is specifically useful for the Site Admin or System Admin roles that create content, but don't publish the content at the point of creation.
The only current filter that tries to accomplish the action above is the "approval" filter, but that requires that a Contributor create or edit the content that is being queried.
Current clients who have expressed a desire in this feature are:
This is something that we've asked about too (ALLDATA Support). It would be hugely helpful!