Your ports sound typical of many plastic ports installed by the OEM in fiberglass boats. One company I am familiar with here in Southern California, Mark Plastics, has the patterns for many boats manufactured in the 70''s and 80''s here in California.They make replacement ports for many boats. If you could give them a pattern of your boat''s ports, I believe they could probably come up with a suitable replacement.
It would be worth your time to contact them at (909) 735-7705. Ask for Mark Heacox, he is sailor, a nice guy, and very knowledgeable.