Hi ,we could sure use some help, recently at a train show in Winnipeg Canada my son and I purchased a 4 piece set of ho Bachmann Amtrak set 1 powered engine bullet shape  2 passenger cars and a dummy bullet, we are trying to find traction tires for the engine and are having no success. we have tried ho universal 12 mm from parts store but they are too big, can anyone help us out?  Thank you