They're from the Solomon Islands! j/k
A lot of people seem to be under the impression that SI percs are all onyx-like. However, I've seen just as many PNG percs as SI's that exhibit onyx characteristics. It seems more likely that the amount of black coloration on the fish has more to do with the depth at which the fish was collected than its origin.
It's hit or miss, don't buy an SI perc sight unseen expecting an onyx. You'll likely be disappointed.
As far as the care in which SI percs are collected/handled in relation to other areas, I don't have any information on that.