Or you could apparently request them. When PFE started with mechanical reefers, they used the "original" type ends at the A end, since the barrier between the interior and the mechanical compartment had to resist internal load shifting, not the external end. The PFE order summaries say that these ends were purchased new from SRE, in the early 1950s.
I think the other issue is the need for a square corner end. As far as I know, the Improved Dreadnaught design was never offered with square corners, as the industry had long realized the utility of the "W" section corner post... but, when trying to fit new ends to existing wood car framing, square corners work better.
In the case of the PFE mechanicals, the likely issue was wanting to use the thinnest corner post possible, which would allow the widest possible equipment access door/panel, whatever you want to call it.
Comment about the Union Metal Products ends... I thought these were all "innies", with the stiffening swales inward from the plane through the corners. I thought the change to "outies" was concurrent with SRECo. acquiring this line.
