Valley, a British maker of complete kayaks, also sells their hatches seperately. My local kayak shop carries Valley kayaks, so getting parts here to the states shouldn't be a problem.

Your biggest problem will be creating a flat spot on the deck of your kayak; both VCP and Valley hatches require a flat mounting spot. It can be done, but it requires cutting a hole in the deck and fabricating a plug that mounts to the underside of the deck, matching the deck's contours, and creating a flat spot to mount the hatch.

Good luck!