Saving seed from Maori potato's

[Rosco]

For the most part this is directed towards Tom but others may be interested.
Here in NZ we have a few varieties of what are called for a better name Maori Potato's.
Spud's to us Kiwi's.
Most tend to be purple throughout with some having deep eyes and tending white as they approach the centre.
I kept a few fruits which the occassional one threw and would like to try growing them from seed.
As we can't exchange tubers due to quarantine restrictions perhaps we could try swapping save seed as we do Tomato's.
Maori Potato's are believed to have been bought to NZ by the Maori from Hawaiiki.
If Itried this perhaps I could exchange seeds of these fruit with the long finger types we don't have here or some of the blue varieties.
First however I would really like to know how Tom and some other enthusiasts collect the seed.
I've looked at some articles but would really like the advice of you real pro's on such things as when to remove the berries and how to extract and store viable seed.
I'd also be interested in what its storage life would be.
Once given that info and you think it worthwhile I'll make a concerted effort to aquire as many of these heirlooms as possible.
Cheers.
Rosco