Yes, that is a repro item ,which I hate. The club did make a batch of proper repro ones some time ago, but they all sold a long time ago. I think your best bet is to modify a current one and rechrome. I dont know of anyone who makes a decent one
I would have thought that if it only binds when the top ring is tightened it points to the bore in the top casting that the choke sits in being where the fault originates. Either it is worn/machined out of true or the tube is wrongly machined/ off set.