As mentioned above, it's common to shop make throat plates and the complexity is saw dependent but usually nothing a wood worker can't manage. My son's Rockwell mod. 10 is different than my 1947 Sears but both have been accomplished.
If using wood, 2,3 or 4 outlines can be cut out simultaneously by stacking the blanks and paper joint gluing together for the cut and final sanding to fit, then pop those apart with a knife.
Paper glue joint - a couple of half inch squares of craft paper between each blank ( brown paper bag ) with a couple drops of Elmer's on each does it ) to hold for cutting out with a band saw or Sabre saw.
As wolley mentioned you then have several for different width dadoes. There are any one of several methods to hold the plate in the saw table while raising the blade up making the cut. Research that to determine which you prefer.