You can make them
You can purchase smoked plexiglass (1/4 inch) for about $8.00 per square foot. I did this on the boat I just purchased. Once you have the plexiglass you have several options to install it depending on your abitlities and/or how fancy you want to get.Simple way:Cut the lower plexiglass the same as the old wood one. Then cut the upper one a little longer than the old wood one so it overlaps the lower one and reduces leaking into the cabin. You screw some teak handles (similar to the companion way handles) on the front of each piece of plexiglass to facilitate removal and your done.Fancy way:I am framing each piece of plexiglass with teak (all sides). The teak frame will fit down in the existing hatch groove and will give a much more water-tite seal. The upper and lower hatch pieces will be tongue and grooved to fit together with the upper hatch having a drip trim over the joint to keep water out. This method requires cabinet making equipment to do right, but results in a tight, rattle free installation. Advantage to plexiglass is it lets lots more light in. Other than that, I can't think of much difference to that and just replacing it with teak plywood.If you're interested, I could take some pictures and do a drawing when I get mine finished.