You have gone further than I ever have but in the interest of educating me and the rest of the PSc collective I'll ask if strength of SS 316 v. silicon bronze is a factor.
As for a source I've found Bolt Depot - Nuts and Bolts, Screws and Fasteners online
has a good selection. There's also McMaster-Carr
- both I've used with high satisfaction although I didn't check if they had you specific request.