Just off the top of my head: You could use Pligg to start your own social news site around your own specific niche.
John Battelle used to use this on his blog: People would vote on what they thought were the best posts he did. It was real time reader feedback.
In truth, however, this question jumps the gun a bit. Local journalists will have a harder time than national journalists -- then again, perhaps that's only the state of things right now because local journalists haven't brainstormed about it.
I expect more niche to form in social news sites: WIth Reddit opening up their API - anyone can create their own sub-reddits now. I could literally create a "San Franciso Giants" reddit -- dedicated to stories all about the Giants.
In Newsvine you can create groups -- and invite people into them. I am a member of the web 2.0 group and the Citizen Journalism group. No reason why a journalist could just create a "TK beat" group.
I expect more social news sites to allow more freedom in this sense.
II keep reading about using all the social stuff but then, working in a specific geographic area, i find it really hard (not to say impossible) to put that into practice. Maybe it's just my case. We can see it's a bit different from the US because you even managed to create groups here dividing you in different geographic areas. It might be just a matter of time until what's easy for national journalists becomes more accessible for local ones as well.