Is it possible that your dad registered his 214 in the County Courthouse where he lived at the time? When I retired, they recommended that we do so for this specific situation (another fire in St Louis coupled with us losing our 214). Of course, that was a long time ago, but it might be worth checking.
I will go check the county courthouse when I get to her town tomorrow. Maybe they will have something. Among his papers, we found an envelope that had “DD214 - do not lose!” written on the outside in mom’s handwriting. It was empty inside. Devastating. We will keep searching.