NeweggBusiness - 20Pcs 3.3mm Hole Dia Plastic Push Button Tactile Switch Caps Cover Keycaps Protector Black for 6x6 Tact Switch
Amazon.com: Gikfun 12x12x7.3 mm Tact Tactile Push Button Momentary SMD PCB Switch with Cap for Arduino (Pack of 25pcs) AE1027 : Industrial & Scientific
20 Pcs Plastic 12x12mm Pushbutton Tactile Switch Caps Cover Keycaps Black for 12x12x7.3mm Tact Switch - Walmart.com
Plastic Button Caps For Square Top (10-pack) - 8mm Diameter : ID 4228 : $0.95 : Adafruit Industries, Unique & fun DIY electronics and kits