At the risk of being redundant, and the fact you might have already been here, try this web site as a starting point.

I would also contact all the major networks (phone numbers are available doing a search on the various networks on the net) and ask for the name(s) of the talent coordinators for the particular shows you're interested in writing for. Now while they probably won't take any info submitted directly from you, ask them to recommend some agencies that they deal with, for you to contact and gets names and numbers (then you can say you were referred by so and so at [name of] network when you contact them.)

Next, do a search on the net for Publishers (or pull out a bunch of paper backs you've got lying around and get the info within them - finding addresses and phone numbers on the net shouldn't be difficult), and contact them and ask for some names of literary agents they deal with, with contact names and phone numbers, and contact those people and say you were referred by whoever at the publishing companies, and so on and so on.

Best of luck and let us know how you make out.