Any machine/welding shop should be able to make one for you in stainless steel to your exact specifications. It might even be better than a generic "off the shelf" compromise. Good luck and good sailing.
"And those who were seen dancing were thought to be insane by those who could not hear the music."
Friedrich Nietzsche, Thus Spake Zarathrustra
If you are replacing the mast, LeFiel in LA made the tabernacle masts for the Westsail's. They may sell just the base if you want to do it yourself. Would need the base of the mast radiused and reinforcing gussets welded on where the axle passes through.