I believe they were a factory/ dealer accessory. They are listed in the Mopar Accessories catalog dated September 1991. Apparently there were also stainless ones available.
@Gjeep sent his to S&S Bumper Repair in So Cal. Half way down page 4
https://comancheclub.com/topic/74144-project-slippery-slope-–-a-’91-mj-runner/page/4/#comments
Sounds like a good deal if there’s no rust and the body is straight. Everything else is “easily” fixed. That brush guard looks to be upside down or something.