Hall, if this is a regular sliding
hatch cover? Shouldn't be any problem, after all, he replaced it once before.
Sounds like either the PO or a cople of his crew were just a wee bit too large and couldn't keep their footsies off the main
hatch.<G>
If the stainless fits, and if there's room....you might take some pictures to a local plastic fabricator (plexi/polycarbonate shop) and ask them about fabbing a new one from a sheet of polycarbonate instead. Much stronger than plexi, possibly much cheaper than having one fabbed from fiberglass.
I doubt you'd find a real replacement unless you can find one from a boat breaker. The places like sailorman are your best source to try tracking one of those down--but it could take a while.