Yes, they do exist. Terry Michael, head of the Washington Center for Politics & Journalism, has started a blog called Thoughts from a Libertarian Democrat. His first post is an analysis of Massachusetts Gov. Mitt Romney's coming bid for the presidency. After dismissing Beltway dismissals of Romney's chances, he notes:
Romney, I believe, is making a big mistake with too much pandering to the social cultural conservatives in his party. He'd be much better advised to run a general election campaign from the outset, talking to the center, and relying on his electability in a blue state and his Mormon conservative credentials to attract pragmatic Republicans to his bid for the nomination.
Whole thing here.