Can you post a picture of the nut that you have and the headshell slot, some type of measurement would help too, I have several of these around the house, you typically get new ones with every cartridge.
If I don't have one you can try
here I bought a couple of cartridges from him, he had some new old stock Pickering XSV 3000's a couple of years ago.
I see he does have a headshell for your Stanton, but show us what you need maybe I have one to mail to you, he wants $36 for the headshell.
Jim