The Corally SP12X T-bar will not work properly because it use some plastic inserts instead of the plastic hub with the metal ball.
I have a couple of Kawada M300 Rsw, but I'm in Italy (not Japan
Here in Italy there is a shop that sell kawada parts but I think that the cost of the spare and the shipment is rather high due to the current Euro vs USD exchange rate.
sells kawada parts, however i think there is the same problem.
Another solution is to buy some spare fiberglass (or carbon composite) sheet and find a generous guy with a milling machine.