I have a 71 CB500 K0 that the tire size is supposed to be 3.50 x 18 from what I have read. The problem is that I cannot find a tire in that size. Does anyone have recommendations on where I can get a stock sized tire for this bike? I would like an older styled tire, but at this point will take just about anything that will fit. I bought a k70 for the front because I didn't think I would have to replace the rear, but have since changed my mind and can't find a tire in the right size. Thanks for the help