That's the part I'm missing on my lathe, too.
As soon as I can get one drawn up and made, I'll be glad to share it with you. Don't hold your breath! It maybe several months before I get it done. I have a full plate right now of work I have to get done before the first of the year. If I have break during this time, I'll try to do something.
I may have one! I had a chance to work on the lathe this evening and I found this in the cabinet
Looks like the previous owners made something that looks like a "c" to replace it and threw this in the cabinet with some other parts.
It looks worn on the sides and the diameter of the pin is somewhere around .360. The hole in the shaft in this lathe measures .376.