Keep barrows, trolleys and equipment rolling with replacement tubes and tyres from Easyroll, rated to 230kg. You can replace a worn tyre or tube on its own rather than the whole wheel, as the buyer's guide notes under wheelbarrow wheels.
The butyl rubber inner tubes cover 2.50-4, 2.50-6, 3.50-4, 3.50-6, 4.00-8 and 6.50-8, each with a bent valve, and the rubber tyres cover every one of those sizes except 6.50-8, all in black. Read the size off the old sidewall, then match material and load rating to your duty.