There are companies that can custom make any shape/size portlight frame and lens you might want.. That would be the best solution but not necessarily the most cost effective.
Unlikely you'll find a source of identical replacements anywhere else, though.
You could change to screw/bolt/glue on acrylic ports attached to the outside of the cabinsides, the sealant Dow Corning 795 has proven effective with this type or installation. It would require you to make a trim ring for the inside to look nice, but it also allows you to update the look a bit as you could design a more contemporary portlight shape.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"