If you can't find a original one, particularly if you have it always down like i do, should not be too difficult to make one, yourself or a pro.
Thats what i would do if i would miss mine, Okume or similar marine plywood with 3 layers of mat on both sides and then sprayed with gelcoat or a quality paint.
Non-skid can be done with special glass pearls, fine sand or bought ready to paint.
Chris