There are a couple of different ways of doing this. Let's see if this one will help: Every city has one or more offices dedicated to assigning numbers to the telephone wire pairs. These offices are called DPAC offices and are available to service reps who are installing or repairing phones. To get the DPAC number, a service rep would call the customer service number for billing information in the town that the number is located in that he is trying to get the unlisted number of. (Got that?)
The conversation would go something like this: "Hi, Amarillo, this is Joe from Anytown business office, I need the DPAC number for the south side of town." This info is usually passed out with no problems, so... if the first person you call doesn't have it, try another. REMEMBER, no one has ANY IDEA who the hell you are when you are talking on the phone, so you can be anyone you damn well please! When you call the DPAC number, just tell them that you need a listing for either the address that you have, or the name. DPAC DOES NOT SHOW WHETHER THE NUMBER IS LISTED OR UNLISTED!! Also, if you're going to make a habit of chasing numbers down, you might want to check into getting a criss-cross directory, which lists phone numbers by their addresses. It costs a couple hundred bucks, but it is well worth it if you have to chase more than one or two numbers down!