3/4 synchro

I restored my 72 Duster #'s matching about 5 years ago.Total rebuild on engine and A-833 4-speed.After a couple hundred miles the 3/4 synchro failed,grinding badly on the downshift.Took it back to to the tranny shop where it was rebuilt and had it torn down and replaced synchro again. About a hundred miles later the same thing happened again.They said
the synchros all come from China now and they would not fix it unless I get an original one or one made somewhere else.The synchro is called a 3/4 Kingomatic.Can anyone shed some light on this problem or know where to get an aternative synchro.Thanks in advance.

72-34--4speed