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On the caphalopod page at the very last link is has a blue ring octo, but the scientific name is o. cyanea, the pic is of a blue ring and isn't for sale though. :? http://www.dal.ca/~ceph/TCP/sources.html
You could try suppliers in south east asia though chances are they won't know the species, you could try getting a bandensis too but cuttles don't seem to be in season. Hawaii would be the better choice.
Yep, for having the pleasure of working on O. cyanea last year in Indonesia i can confirm that they grow really big . In my study of the local octo fishery, i (only) came across (by that i mean the octo was brought to me for statolith removal by a fisherman prior to being sold to a middleman) a 3.2kg octo. I've had access to the local middlemen books and it seems the record stands at about 6kg ... but it was caught two weeks before i arrived on site dang!