Del, according to the Parts Book, that"s a "Plate, Ignition Switch Index", Part No. 181389M1. (We didn"t get one on a TO-20!)
If you do a Google search for that part number, you"ll get results for Ritchie Implement in Wisconsin; however, it says that part is a "decal", so I"m not sure what"s up. (608)623-2331 or (800)726-7278.
I was just recently in contact with Ritchie Implement, to get an OEM pivot pin/bushing for the TO-20, and they had a good price on those items.