Do you mean just the bullets?
There are many fine bullets made for the .45-70, both jacketed and cast. Any bullet of the proper diameter can be used, but examine what it is you want from that bullet.
Look at the velocities the .458 SOCOM runs, and the bullets it uses. If you can get those velocities from your .45-70 (SAFELY!!!), then you would get similar performance down range.
The Sharps is not the strongest of .45-70s, although it will handle more than I would put in a Trapdoor Springfield, its not a Ruger.
I admit, I don't know much about the .458 SOCOM, but isn't it made to give (standard?) .45-70 ballistics from an AR class rifle?