Is one fixture not working? Why are you looking to replace the entire fixture rather than the bulb?
If it was me, I would first of all plan to change out ALL of the fixtures for the new, more efficient, cooler LED lights, but first I'd measure (precisely) the cutout opening then go to Amazon and do a search for "12V RV puck light" and find a style you like and that will fit the existing cutouts in your coach. You'll likely also want one that will cover the same area that the SILVER part in photo 2 covers, since it's likely some discoloration has occurred.
Amazon as well as specialty RV stores have lots of choices and I'd think you could find something to suit your needs with just a little research.