Venator, I am really glad that you find the comparison useful. But really, Souten is so similar to Sky High that I am sure that you will be happy with it. And if we're lucky, Sailor just might decide to bring back Sky High in a few years as they seem to be doing with their Jentle inks range (the cycle seems to be 4-5 years).
As for the Sailor ink supplier in Australia, I really haven't been successful finding any that sells these inks at reasonable price. So I always go to eBay for Sailor inks , and I can recommend seller called "cool-japan". Even if some inks are not in stock just contact Atsu and he can get them in for you in most cases.
There are also some sellers on eBay that sell the inks a lot cheaper but I haven't tried them so I can't comment on that. Good luck!