I used 18-gauge (1.0 mm) aluminum sheet for my blank, but you could use other metal sheet, like copper or brass.
Using a jeweler's saw and a 2/0 blade, cut your strip of metal sheet to size. You could also use a bench shear to cut the strip.
Holding the strip against your bench pin, use a medium-cut, flat hand file to smooth the corners and edges of the strip.
Use 400-grit sandpaper to refine the filed edges.