Amazon.com: LEGO Technic Turntable Platform Gear : Toys & Games
Amazon.com: LEGO Technic NEW 12 pcs LIGHT GREY WORM AND RACK GEAR SET Screw Track Kit Part Piece Mindstorms NXT robot robotics assortment pack ev3 motor : Toys & Games
LEGO Parts: Technic, Gear Rack 1 x 13 with Axle and Pin Holes (Pack of 2 - Black) - Walmart.com
Excellent Lego gear tutorial by Sariel: gear ratios, types of gears, best practices, etc. : r/lego