This is a sample model of the mechanism that converts the rocking motion of the lever into the rotary motion of the gear. The gear will not rotate smoothly but in steps.
 

Other necessary components: 

• 2x screw M3
• 1x spring D4-20 (from ballpoint pen)

Printing parameter:

• Nozzle: 0,4 mm
• Layer height: 0,2 mm
• Perimeters: 2
• Infill: 15%
• Supports: None
• Filament: PLA