If it's thin, say 1/16" you can cut it with a razor knife and a straight edge.
Thicker than that, I'd use a hacksaw with a 32 TPI blade.
This is all assuming we're talking about relatively short pieces, like riser accents or tip overlays.
If I were to try to narrow, say, one of the 39" pieces like Binglam's sells, I'd either do it on the bandsaw with a metal cutting blade or sandwich it between two pieces of scrap wood and cut it on the table saw. A guy would probably want to set up some finger boards to keep the pieces from sliding around with that method.