Well, no consolation for you, but you're not alone. I, too wish Metro would take the business risk, and make the investment for rear panels. As already noted, white panels are especially subject to damage......
One thought I've had is to take an old panel and try and use some textured paint to see how close I might come ....... I even tried to "soak" a paper towel in SEM white paint that I thought was close in texture to repair a small section. I ran out of paint and never finished..... But I thought I was getting close. Also, there are cheap textured paints now, although I'm unsure if re-spraying over them with SEM white afterward will work.....
Perhaps all a waste of time and a few $$, but we don't have any good options......
Vt Mopar