All Horizon Hobby owned brands maintain part numbers internally for almost all parts. Granted, there are a number of 'exceptions'...but, with many "parts groups" sold under a single part number, many of those individual parts can be purchased separately. The way to find out if the part in question (or any individual part that is normally part of a "parts group") is available separately is to contact Horizon Hobby Support.
Now, here's where things might get a little 'tricky'. Because of the pandemic, Horizon Hobby has suspended phone support for incoming calls. Prior to the pandemic, I would just call, explain the situation, they'd figure out if the part was available individually...and, if so, an order for the individual part would be placed (and, if not individually available, you'd either have to order the "parts group", or they might help you find an 'alternative'). Unfortunately, right now, the only 'incoming' support options are via email (submitted through the support page), or online chat (which isn't always available).
There is a "plus" side to this - if they determine that super is needed to be provided over the phone, them they will call you. The reason (which should be obvious) incoming phone support has been suspended, and went outgoing phone support is extremely limited, is due to a personnel shortage (as is the case with many companies). You do have one other option: measure the ball stud in question (as the vehicle will have others of the same part), sand figure out who else has ball studs of that same sizing.
~ More peace, love, laughter, & kindness would make the world a MUCH better place
