Include your title, profession, specific experience, etc. Send your address and phone number with the letter. The media will call to confirm who you are if they are considering using your letter. Check in the written material itself for that information. For radio and TV, the end of a program often produces such information.
Most media outlets have their own websites.
The General Secretariat is in New York. This site is maintained by the Foreign Policy Association and you can put in your zip code and get your congress people's names etc.