Just got off the phone to A2 customer service, they indicated...

Just got off the phone to A2 customer service, they indicated they are having no issues with deliveries to supermarkets. That is, the deliveries haven't stopped and A2 in fact have recently doubled deliveries to them over the past few weeks to try to keep up, however as the limits were increased from 2 to 8 tins per person they've seen the shelves cleared of stock. They indicated that they aren't in control of customer limits at the supermarkets.

Any one can purchase 3 tins a week off the website and will even supply a free shipping code if you can't get a tin at the local supermarket and they can verify that it is empty. This appears to confirm what everyone else has said regarding the increase in demand.