You will need to know what network the station is on, and the station "call letters." The specific news show may also have a "catch name" that would help.
Few listings appear to be available using "Channel numbers," probably because cable and satellite services frequently map programs to different numbered channels.
As a quick-look example, the above site gives a "clicky" to ABC, whose site has a "local program schedule" clicky. From there you pick Washington DC, and several of the stations have "email us" addresses. Right-click the clicky and you can read the "target address."
Should be enough to get you started.
If you're in the area, there is probably also a "Chamber of Commerce" or "City/State Information" web site that should have links to tv stations, or just put the station call letters (WGXX or WBXX-tv) into a search. In Internet Explorer (newer versions), you can just type the call letters in the "Address" bar at the top, and it will search for it.