It's difficult to find real examples of very low frequency passive forms - by definition. So here's one I heard recently that was produced perfectly naturally,in context, in a Sky News report:
it was highlighted to police that in this house dangerous dogs had been being bred.
Sky News 30 Nov 09
Say it aloud, as a news reporter, to get the right sound.
The corpus linguist's best friend, Google, offers 5 more examples, using bred, and the WebCorp Web Concordancer and Collocation extractor really only offers "for" to the right as a significant collocation.