from what I read in that thread, it looks like they are a real pain to remove. not sure I could be of any help if I saw one in the junkyards.
found another left on ebay: https://www.ebay.com/itm/Mopar-Left-Belt-Retainer-Reinforcement-55175755AC-For-97-06-Jeep-Wrangler-TJ/232734456328?epid=1141786490&hash=item36300dfa08:g:IY8AAOSwtrha0qgc:rk:1:pf:0