If you find any source I would be glad to learn where. I have three 2nd gen wagons, each of which have rear bumper covers that are cracked, with parts glued back in after they got broken away. I also no longer sit or kneel on them, and use a chunk of 2 x 4 wood lying on the top when lifting heavy items into/out of the back. With one of mine the bumper got smashed so badly that I made-up a 'sort of' replacement. I posted about it in the wagons subforum, back in august of 2017 complete with a photos. I started with a rear bumper for a hatchback, and after replacing the six studs holding it to the car with studs that were an inch longer (cause the rear of the wagon is thicker than on the hatchbacks and sedans), I used a saber saw to slice way the top of the bumper, so the gate could open and close. From 20 ft back it looks okay..
My postng is about on the 4th page of that 'wagon' subforum, with the title "My wagon bumper effort".
Good Luck!
Be sure to go to ebaymotors(d0t)com when searching for bumper covers. I have gotten 3 or 4 front bumper covers from them over the years; tho currently the supply seems to be zero. I also own three escorts that are hatchbacks.