I called VTI. They didn't have a screw and nut specifically for the 1858 buffalo model, but they compared the 1851 Navy hammer screw and a regular 1858 hammer screw and said they seem identical, head size, thread, etc. They're sending me an 1851 Navy shoulder stock hammer screw and nut, free of charge, and want feedback as to how it works out for me. What a good company!
Liberty and freedom often offends those who understand neither.