Need a disconnected phone number for a Halloween prank.?

I'm planning a very elaborate prank for my annual Halloween party this year. Part of the overall plan is to have my cell phone programmed to dial a phone number that has been disconnected. How do I find such a phone number? In my line of work, I encounter a number of disconnected numbers, but I'm sure eventually the number gets igned to a new customer. Is there a novelty service out there somewhere (like the rejection hotlines) that I can call and be ured of getting the disconnected number message?