Not knowing where you are based it is difficult to help. Paintcraft in Nottingham would be able to repair your trolley but you might find it cheaper in the long run to buy another. Were you in North Yorkshire I know someone who could do it. A new axle welded on would be circa £230 you would then have to get it re-galvanised.
If your axle is made from angle iron you could buy another piece of angle iron to nest inside the existing one and bolt the two together with 6mm high tension bolts at about 150mm centres and staggered.