Currently there is no tab for such question, despite at least one feature request asking for one. I don't really expect a tab to be added, mostly because the functionality itself is already available.
Simply use the search term hasaccepted:0
(as the whole search or appended to your search) to filter the results to questions that have no accepted answer. Using it on its own allows you to find all such questions, whereas including other search terms/conditions allows you to be more targeted.
On the /search/search page, there is an "Advanced Search Tips" link to the right of the search button. Clicking this will teach you about more search magic.
As far as actually getting this implemented, I'd suggest upvoting (and perhaps putting a bounty on) the Meta question I've linked (although there is never a guarantee).