Your boat is new enough that you can get it from your dealer, but as Fish mentioned, it can be done cheaper other ways. Any local upholsterer should be able to match up the vinyl and build the cushions.
Why is this a fiberglass part? Wouldn't it just be a sectional board that lays on the "lip" and the cushions set on top of the board? You could do this as simply as you want... plywood. Or use PVC board or starboard.
Thanks for the response. I should have been more clear. I am not really after the cushion (though I would not mind having that too) but more so the fiberglass blank with the non-slip texture that fills in that area so, with all cushions removed, I can stand up there to fish and throw cast net. Just want more platform