First4spares 12" Solid Wheelbarrow Wheel, Tyre & 1/2" Axle Reducer Bushes for Garden Trolley/Barrow/Go Cart/Trailer Truck : Amazon.co.uk: Business, Industry & Science
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