CR machine (Fred Chelminski) does crank work I THINK....don't know if he sells balanced cranks or not. Arrow is another possibility.
Also not sure if MotorBicycleRacing or Dax sell the cranks separately or not.
PM MotorBicycleRacing here for more info or see Dax website.
(I own a GenV 40mm stroke/pk80 style engine from MotorBicycleRacing and it's a sweet little bullet!)