@ Dr. T :
the tires are from Duro. I got them from a Cycle store her in Hamburg Germany or you get them from here http://www.chopperdome.com/shop/5/1/0/0/70/0/0/19220/Monster_Tire_24_x_4_including_tube_and_strip
But i think you dont want to import them to US. I think they came from US try google...