I found the black poly Joiner and Bushing OK but he looked at me funny when I said, "PVC with a 25mm ID and a 32mm OD"
Same with the "Pressure Coupler", he needed an OD and ID for that and it didnt look anything like your photo of one, without the mast tube in hand I didnt know what on earth I wanted, still dont.
However, Mal from Sunstate Hobie has a Mast Tube he will give me and also has a Collar in stock.
As I said you need to have the Hobie parts with you when you are trying to get the plumbing parts.
There are probably other standard plumbing parts that will get the job done. I just happened to have the pressure coupler at hand. I went to Bunnings with the Hobie bits and after a bit of trial fitting had the off the shelf bits needed to finish the job with very little modification.
The benefit of the standard sail is that it can be easily stowed in the hull when in kayak only mode with the mast in the paddle holder. The near 16' mast cannot and I imagine it would be very tippy even with the sail furled.