Floor corners

Hi all
Working on my 68 cuda vert floors. The rear floor corners (under the back of the rear seats) are rotted right in the corners, about 4" square. Very solid aroun the holes so I would like to just cut out the affected area and weld in new corners. Problem is I have no way to fab new corners and don't find them on any panel repl. sites. Any ideas?
Thanks
Pike- the holy