I can't talk for other airports but a position at Sydney as a duty manager would require years of work, a fair bit of grovelling and a knife or 20 in the backs of all your best friends. And that's looking at it in a positive light. I assume all other major city airports, generally being largish corporations wouldn't be far off either. For what it's worth however smaller airports like cooma, broome and camden have had positions available like this. I think these positions are quite general (from taking a/c regos to polishing the rwy edge light bulbs) however are probably a bit more accessible. Then again you could always try airlines or ground handlers and see how you go there.