Welcome to the Forum! These fixed ports were popular and Catalina Direct is one possible source for replacement gasket kits. Search this Forum and you'll find lots of references and experiences for dealing with these ports.
I have four of these ports on my boat and I have re-bedded one so far. I was able to re-use that gasket. When I removed the port I found the outside frame gasket was just an open-cell foam. Outside, on the glass/frame joint, was clear silicone bead that was not doing the job any longer. On re-assembly you have to be careful not to break the glass (if it is a glass pane) as it and the gasket make a tight fit, and then decide how to bed the frame. I used 3M 4200 under the frame and a bead of black 4200 to replace the silicone bead. On my next one I will switch to 3M 4000UV for the frame. Others will advocate butyl tape sealer and that works also, with somewhat less mess. At the same time I replaced the badly deteriorated plywood paneling in that section of the cabin.
Craig