That is interesting. But you know Aussies also use words that UK or America don't have.That's really odd. I am an Aussie transplant now living in the US but kept chooks all my life even living in Australia and we always called them roosters there. I have some English friends here and they call them roosters too, even though I never hear them using much in the way of American lingo.
To the OP, I wouldn't change the classifieds except to ADD the word cockerel. Since most people think of a male chicken as a rooster, you might get more responses by leaving that word in, and just specify "young male rooster or cockerel" or something like that.
UK people also don't use the term 'Chooks'. Maybe the English friend call them Roosters in Aussie as that is what they are called there. I now call them roosters as most of my fellow chicken keepers are American and I don't live in the UK now, so its easier.