2003 Mitsubishi Montero Sport 3.5 the crank pulley bolt loosened up and sheared off the pin where do I buy the roll pin? And how do I know if I'm getting the updated bolt?

 

Have you inspected the timing sprocket and harmonic balancer for damage to the keyways? I had this happen to me and it destroyed the keyways leading to me having to replace it. As far as just replacing the rollpin, I believe your best bet would be to have one fabbed at machine shop but if I'm not mistaken the rollpin and timing sprocket keyway are interference fit, meaning one part needs to be real cold and the other real hot so that when they cool/warm they are practically immovable.