the one screw in type should be available from a variety of places. They are used in small sail boats as inspection ports. You just have to find the right size.
The other one you might have to make. You could laminate a couple of thin sheets of plywood over a form to match the curve and glue some sheet rubber or wide weather stripping to make a seal. That's how some plywood seakayak hatches are made.
These may not be the right size but this is what to search for.
check westmarine as well.
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