Hi GY,
Try this: http://www.caboosehobbies.com/catalog/
Search for traction tire
They are Marklin, someone else might verify that they'll fit.
They're cheap anyway!!
Billk, you are right. I had problems with tires all the time, then went to an orthodontists office and the gave me a bunch. The only thing they asked was, "what size do you need?". Haven't had any trouble since.