Jethro,
Are you refering to the shift fork? The bit that looks like a horseshoe on the inside and is conected to a shaft that comes through the cover plate onto which the shifter linkages are bolted on to?
If so searching for "muncie shift fork" comes up with a number of vendors, seen a few for sale on US ebay too.
I've broken a few of these in the past with my old muncie, apparently they don't appreciate the finer points of flat changing.