Rob,
They’re fairly widespread in the western Pacific Ocean and can be found from the southern tip of Japan to northern half of Australia. Rarely have I ever seen a Harlequin Tusk made available from a verifiable source other than Australia, Indonesia (Bali,Jakarta,Java,Sumatra,…too many islands to list...), or Philippines. It is possible, but not probable, that a specimen could be from another area. The bulk of what is in the trade is from the previously mentioned sources.