Of course they make 50s Chevy and Ford corners. You might look at all those and find the one closest to the International. Then if you are fairly good with an anvil and ball peen hammer (or body tools if you got 'em)you might be able to reshape them to fit.
Willys36 has the right idea. Make a template of posterboard of the curvatures of the bottom corners of your cab, then check it against a Ford (48-56 probably) or Chevy (47-55 1st). If they are close you can certainly modify them, you'll just need the tools and the welding skill. If you do't have it your local quality bodyshop should have someone who can handle the job reasonably.
Best of luck!
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