Hey Oaky,
If you can create a sketch, you'll find quite a few fabrication shops willing to quote the part to you. You'll want a fab shop with a shear, a brake (for bending), and a punch (some shears also have a punch). If you can get away without countersunk holes, you'll save money...
I checked my 1951 Marks Standard and Woodruff keys are referenced by the 204, 304, 305, etc. numbering system. Must need to go back quite a way to see a #91.