I don't think what you're seeing has anything to do with it not running right ,Don't get locked into this as the problem , I really doubt this is anything but normal wear / tear in a chainsaw that has seen use. I would look at your fuel system first , your compression is good so cylinder scoring...
Any pully the same size will do in my opinion , it's not something you need OEM for , just make sure it's the same diameter and same size groove for the belt.