Sorry it took me so long to reply, I've been out of town.
Here is a link for Comedy Central-
Comedy Central:
Usually at the beginning and end of a program there is a little blurb that says who is paying for the captions.
Info from NAD-
Television - National Association of the Deaf
Also, I'm writing to companies who produce DVDs to remind them that subtitles are not the same as captions. see-http://joeclark.org/access/captioning/Neves/
But to find to whom I should write I usually just google the network and email the "contact us" thing.
Also, writing to politicians could work.