Marathon Universal Fit Pneumatic (Air-Filled) 14.5-inch Tire and Wheel Assembly, Replacement for 4.80/4-8; 4-8; 4.80-8; 4-6; 3.50-8, Wheelbarrow/Cart Use, Castle Tread in the Wheels & Tires department at Lowes.com
2 Pieces Rubber Caster Universal Wheelbarrow Replacement Wheel for Wagon Hand Truck Mower Cart Replacement Tire Luggage Wheel - AliExpress
Amazon.com: 6 Pack 13" Flat-free Replacement Tire Solid Polyurethane Tires and Wheel Assemblies 3.15" Wide Carts Tires with 5/8 Inch Axle Borehole 2.1" Hub for Wheelbarrow Garden Cart and Trolleys : Patio,