Are longer threaded stainless eyes available? If so rather than try and get a thin bit if stainless you could carve a block of hardwood and fully encase it in fiberglass in the boat and run the bolts through it.
To get a pattern of the shape, could you use thin copper tubes (or other easily malleable material), set at defined vertical distances apart, bent to imitate the horizontal contours.
I have used the very strong aluminium catering/disposable roasting dish type things to form a curved pattern. It holds a pattern well .
if you wanted to get really creative, somebody could cast a curved piece from a template.
or a grinder / power file on a very thick slab of stainless and then profile it?
no idea how hard grinding a slab of stainless might be.
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