You can try this guy. Not sure if he's still making them or not.
http://www.the510realm.com/viewtopic.php?t=17682
Also after a quick search I found a post with this guys information. The post was old so idk if the contact is still good but worth a try.
"Try contacting Mark Grimsley (Arlington, VA area). He has been making both front and rear floor pan patch panels of 18ga. steel for 6, 8 or more years. He also makes rockers. Mark's email:rediron07@comcast.net
and his number is 703-490-2032 "