Hi Ian.
I don't know where in NZ you are but there are a number of excellent
bakers in and around Wellington that have sourdough product and I'd
be surprised if most major cities and good sized towns don't have some too.
I have been making my own sourdough (in Wellington) for about 5 years
or so now and am pretty happy with the results. I am on my third
starter - I don't think I fed the first two well enough.
I have found that it always works best when warm - say 20-22C - but
it does work if its cooler only more slowly. I just left the starter
in the kitchen to get it going - flour and water with a little bit of
slightly fermented apple juice to kick it along. I only use organic
flour and filtered water.
Now my starter spends half or more of each week in the 'fridge and I
take it out and feed it for a day or so before using it. I always at
least double the volume with equal parts flour and water each time
and don't use it until its really foaming.
I have several books that have slightly different approaches. I
started with the Bread Bakers Apprentice and have made Reinhart's San
Francisco sourdough successfully. I now have a couple of books that
are by a NZ baker - Dean Brettschneider "The NZ Baker" and "Global
Baker" and his recipes work here.
If you are near Wellington you can have some of my starter to
kickstart yours if you like.
Cheers,
jim