I haven't seen that style shower door in at least the past 10 or 15 years. Finding individual panels is going to be an impossible task. Finding a door like that may well be just about as difficult.
There are a number of "updated designs" that will fit the space, probably look better and be easier to keep clean. You can look at the various size openings on Amazon and then do some "google searching" to find the best price.
I searched Amazon for "Folding RV shower door" and these came up:
https://www.amazon.com/s?k=folding+R...f=nb_sb_noss_2