You are aware that Ford outsources the rear bumpers. They may make the bumpers for the front, and newer rear, but the rear bumper that came on your 2001 Flare Side was made by outside vendors.
You might check other makes that made Flare Side body styles for bumpers. After all, the only thing that might be different is the mounting hardware.
Look for bumpers from Chevy/GMC S-10/Sonoma , Toyo's, ect. You just need one that is the same width as your Flare Side came with.
Also, google up "chrome tube bumpers"
Many sites come up with bumpers for everything from Jeeps to full size. Maybe you can find one with the right width to fir the Ranger.
I did a bit of google searching, and Ford did offer a painted and a chrome rear bumper for the 2001 flareside Ranger. Chrome is discontinued but the primed/ready to paint are still available. Pricy, but out there.
Ford Part # YL5Z-17906-KA. The part # for the chrome flareside bumper is #YL5Z-17906-HA.
Grumpaw