The reason no one will do that is because you don't really have a third party movement. What you have is a fragmented movement of people who don't like the two major parties. I don't think they'd be able to coalesce around a third party or a coherent agenda. (If they could, then we'd have a viable third party.)
Because of that, it would be hard to create a television station marketed to third party advocates. Whom would you market to? Libertarians? Green Party/environmentalist wingnuts? Socialists? Neo-Nazi types?