1971 Demon 2 Speed Wiper Knob
I've got this extra switch with knob. The knob is not perfect, it may work until you find another one.
The switch itself has part number 3488839, '73-'74 A-body 2 speed for manual washers. The knob itself looks identical to my daughter's '71 Demon with standard dash.
Looking at pictures online, the knob and probably the switch, seem to be the same whether you have a rallye or standard dash. Maybe somebody else can chime in.
Bill