The evening TV News shows - while not exactly *inventing* sources - locate them via a "ringer routine." Let's say that El Maximum Presidente Senor Bush proposes a prescription drug plan. The network, not wanting to say anything good about El Presidente OR his plan, calls up its toadies at the DNC and says something along the following lines:
"Hey, Stan, I need a family, preferably white, halfway prosperous, midwestern, who will NOT benefit from this new drug plan Bush has come up with. I can have a crew on the ground anywhere in 2 hours. Get back to me."
About a half hour later, the phone rings and it's Stan back at the DNC with a number. "Here's a family in Dubuque Iowa. White, Midwestern, wife is a doll but has huge medicine needs. Husband makes 80, but the Rx bills are killing them." The DNC staffer has simply found a prominent local DNC activist family and passed the word to the nets.
An hour or so passes and the local affiliate crew arrives with a list of questions from the national reporter back in NY. A half hour of shooting, some interviewing, and the crew heads back to the station and backhauls the material via satellite to NY, where the reporter edits together his/her DNC hand-fed material.
Then, when the Nightly News comes on, there's that midwestern family sooooo MANY people can identify with with the wife who won't be helped by Bush's plan. This machinery has been in place for DECADES.
Michael