Since they do not expect overseas Vocaloid fans to be able to use or even think about using Vocaloids from Japan, studios such as Crypton basically restrict the sales of their Vocaloids. Amazon of Japan, the main site that Vocaloids are sold on, checks on your country are made when you attempt to order the Vocaloid with paypal. Your paypal details will also contain which country you are purchasing from.
In the past, illegal torrenting was a solution to resolve the Vocaloid problem. However users did not stop there and English Vocaloids, who were downloaded to be able to use the software in English, were downloaded despite not sharing that same problem. Some sites, such as Vocaloid Otaku, began to ban the link sharing of torrents for Vocaloids. Torrent sites also will from time to time purge themselves of Vocaloid downloads, as noted Gakupo is often a target due to his voice being the popular and well known Japanese singer Gackt. However another note about illegal downloads is that users often do not realize that certain Vocaloid copies will need special considerations and treatment, and in the past both Prima and Luka were known to be problematic for users to install. Sometimes these problematic illegal downloads will even affect official versions. As with illegal files circulating, these free copies may be laced with viruses in the worst cases.
There are 3rd party websites that allow users to buy Japanese Vocaloids, however users must be aware that no matter what, if they cannot understand Japanese or are unwilling to properly learn Japanese, there is little point in buying the software to begin with.
As of Vocaloid 3, thanks to the Yamaha on-line shop, purchasing newer Vocaloid 3 voicebanks is much easier for overseass then it has been in the past.