Try John Pierce at Stealth, everyone seems to having problems contacting him but I seem to always get through simply ringing on the landline number about 1.00pm.

Somewhere I have a mast ball foot but not the ball although the early Stealths had a Hobie ball. If you are stuck contact me.

The gooseneck was a casting John had made up, later versions use a standard gooseneck with a simple round Ali tube. It maybe cheaper to replace the tube and gooseneck together. The alternative is have an engineering shop re create as a one off for the oblong shape, you only need a plug with a stainless standard rod end screwed in.