I don't like Hammerite as it tends to be brittle & chips easily.
You could try an agricultural suppliers for 'Implement Paint'. I have used the Sparex range of paints before, with good results. I quite like 'Simba Orange'. You can get details
HEREIt looks like this:
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It tends to stand up to the knocks & bangs very well, but you'll need to prepare the surface well & prime it first.
HTH