No one makes true 1/48 ACW figs (or at least no one was doing so as of last year). Some wargaming figs are close, but they tend to be cast in combat poses and vary considerably in quality.
If you arne't picky about the scale, the hunt will be more succesful. In your favor is that fact that folks didn't tend to be so large 150 years ago, and smaller-than-scale figs can be used effectively.
RR crew can be made out of civiialn figs.