Well, on one I did on a previous house I made it myself. Just cut a 1/2" piece of Poplar (I think) routered the edges, mounted a small handle and hinges. Made it so it flipped in and up. Did not put any type of safety latch (bachelors don't think of those things!!), but I will be on this one as we have a youngin on the way. Haven't figured that yet either:)
Maybe try a home center or lumber yard and see what they if anyone makes pre-fab stuff. My guess is most builders fab it all themselves.