Scott, I agree with the yard finding one as they probably have many sources if they're not to lazy.
If it is indeed unavailable building up the current "boss" an 1/8" should not be a big deal. Most "bosses" are just sorta smooth f-glass anyway. Perhaps a piece of "exhaust f-glass pieces" could be cut and epoxied on the old boss. It just may be faster and again the yard should be able to do this easily.
Dave Neptune