Actually, there is only technically one species of Harlequin Tusk. The two varieties people talk of are where they are collected. The ones from Australia are hook-caught and are muchhardier for some reason and the Figi ones are caught using questional techniques. There is also a similar species called an Anchor tuskfish which is noit very common in the Aquarium because of its lack of good looks. Hope this helps!
I would go with the Australian H. Tusk, and an easy way to tell if it is from Australia is look at it's teeth. If they are solid blue then it is. Good luck, they are great fish. I have had mine for quite a while and not had any problems.