Are you talking about the chain plates? In other words are these U-bolts where the shrouds attach? On the Nic 38, these “hairpin” rods go through the deck and meet a protrusion molded into the hull (we call it a knee).
If you are replacing these, you will likely need to have them custom made. They should not be too hard to make. The purpose of the plate above the deck is simply to act as a water barrier. The challenge will be getting the angle correct, but realistically (and looking at ours on s/v Rainshadow) the angle does not have to be perfect.
You should inspect all the hairpin chainplates – our boat is a similar age, and we found crevice corrosion, although not bad and we did not replace the rods.
You may want to see our writeup at
Pulling Chainplates