Why don't you check out the Morgan owner's site - google "morgan yachts." They may be able to help. I have a Morgan 35 and replaced 4 of the ports with opening ports. Makes a big difference in warm weather. The openings were close in size to standard 5x12 inch ports, available from a number of vendors in a wide range of styles and price ranges. I did have to do some grinding and
epoxy work, but they look and work great. If you just want to replace the "glass", you should be able to take out the aluminum framing - probably just on one side, remove the acrylic panels and go to any good plastic shop to have them cut you a replacement. Check your yellow pages.