I took a look at a few for sale online. This looks like white acrylic.
1) Buy a sheet of white acrylic.
2) Draw the entire shape of the hatch out.
3) lightly score the outline many, many times.
4) Take a very fine blade, like a scroll saw and cut along the score line.
5) Lay the long flat part on a bench, with the portion that needs to be curved overhanging the bench.
6) Clamp along the bend radius.
7) Start heating the acrylic with a heat gun and bend the top radius.
8) Sand the sharp edges.
9) Drill for mounting and securing hardware.
OR
Hire someone to manufacture one for you.
Good Luck