SW, did you talk to the countdowns about why they are out of stock? I really wonder sometimes if they are under pressure from the mainstream industry to make it hard to get.
Re the one-litre bottles of A2, I would suggest you phone Fresha Valley. They are the ones who process and distribute A2, and their website indicates that it's available in 1L bottles. It may be just an issue of whether any of the supermarkets want to bother with smaller bottles just for a few oldies.
http://www.freshavalley.co.nz/fresh_a2_milk.php