David, this is because your anchor comes up through a slot in the actual bow fitting, rather than onto a roller assembly mounted on top of it. Your stainless strip idea would work, but as you say, not that easy to obtain or have made.
What about fashioning your own from a softer, easier worked, non-rusting metal like aluminium, rather than stainless steel..? That can even be cut with good tin snips to get the size and fold points right, then just glue or screw it in place for easy replacement if it wore through over time. I would think the OP might be able to do the same thing with a larger sheet, suitably shaped then folded round the stem, then drilled and screwed it in place. That high up, water entry is not a problem.