Posted 25 August 2013 - 08:55 AM
What I did on the PS2 version of the game to find a Securicar was: going to Staunton Island, finding such a vehicle there, drive it all the way to Newport, take the boat and go to Portland. Then jack a Taxi, go to the avenue between Porter Tunnel and Portland subway station and keep driving back and forth. Spawned a Securicar for me soon enough. So it might as well work for the Bus.
Oh, BTW, you can get a Securicar or a Bus during Firefighter. Because it is on very rare occasions that they spawn in Vigilante (thus making it almost impossible to get during this mission).
On other note, try keep hitting the avenue between Porter Tunnel and Subway Station and the avenue between Punk Noodles and Callahan Bridge to find Securicar, Flatbed, Bus or Trashmaster. They spawn sometimes on these two roads.
Hope I helped.