The best option would be to find a local old-school lawn mower shop w/ that part on the shelf. Another option is Craig's List or Offer Up for an inexpensive compatible machine w/ that part in good shape.
Those parts are also available on eBay, but the shipping is frequently prohibitive.
I have 1 I can sell you for $30. I repainted it this summer. No- it is no where close to as rusty as yours.
Let me know if u r interested so i can strip it down and weigh it to get a quote.
Some U-Pull-It junkyards have a lawn mower section. I know of one in Pennsylvania. If you happen to be walking the Appalachian Trail, it's only about two miles off the trail.