My Nordic originally had heat formed plexiglass edging. I think all the Nordics were made that way. Are your openings oval or square?

When mine deteriorated I made replacements from King Starboard. I cut the centers out and routed the inside edges smooth, then used a round over bit to ease the edges. A router table is essential to to this. After getting the inside cutout right I used a table saw to cut the outside flange. That was about ten years ago and they still look good. Starboard is easy to cut with woodworking tools and it helps to have a friend with a well equipped workshop.

PS. Save the scraps - you will find many uses for starboard on the boat.