No experience with South America, sorry. Possibly the general luggage forwarding services. Or possibly wrap it up and send it by DHL/FedEx/UPS. Neither option bound to be cheap (getting access to a corporate account with DHL/FedEx/UPS helps, though).
For Japan to Australia, you can try the famous takkyubin/kuroneko (in addition to DHL/FedEx/UPS). They do ship internationally, but not cheap. More importantly, they have size limitations which are more restrictive for international shipping than domestic - I believe it was 160cm max length a couple of years ago (they would not ship my powder stick from Niseko to Hong Kong, having happily brought it up from Toukyou a week earlier...).
Thanks. Nuts - board alone is 160cm never mind packaging or the board bag. Me thinks this will not be as easy as I had anticipated!
Limit might be 165cm. Double check with the web-site (or you might need a Japanese speaker to call up takkyubin).
But it is probably going to be tight - my pow board is 163 and with the bag (and some cardboard taped to it - takkyubin only accepts 'packages, not bags/suitcases for international shipping...) it was a few cm too long.
So what did you do when they refused to ship it back, how did you get it back?
We've friends/family in Japan and Aus so getting that leg of the shipping may be expensive (I'm hopping for ideas how to limit that!) but should at least be possible (there's also a near 3 month time frame for shipping, so we won't be looking for express etc).
I wound up just taking it as check-in luggage on my flight.
Beware that the various Asian airlines treat snowboard/ski equipment quite differently. ANA was happy to take anything up to the overall weight limit without extra charge. In contrast, Cathay Pacific and Singapore Airlines were charging something like $100. (Note: At least one of them wanted to charge per set, not per bag. They actually asked whether I had more than one deck/set of gear in the bag, because I was traveling together with my girlfriend and checking in only one board bag).