I can supply the upper tube assembly P/N: 21707-000; these have become scarce in serviceable condition. The sheared turn stop can be repaired, there is an FAA-approved shop in Wisconsin providing this service. I usually have their repaired tubes in stock, EXCHANGE ONLY, on repairable cores NOT CRACKED.
See Service Letter SL-596A
I have 12 cracked cores, Webco Aircraft says they have 25 of them. Someone has to step up and make a repair available, probably the owner-produced type.