I wonder if you could start a face book page with questions and updates and lure these people in to make comments. If they are internet savvy I bet they would take a look and be drawn in especially if you post pictures with sentimental value i.e. hand writing and any drawings in the buss (I bet the grandkids would help and get a kick out of it). Also see if anyone knows who the driver was and if he or any relatives are still around.