The trick for these things are not ordering online. The trick is to walk into store to buy one.
They allocate each store a certain stock, and a certain level of stock arrives daily. Whereas online you go into a queue against everyone in the country, instead of locally.
It's how I got my iPads on launch day without reserving, walk in and buy it. They normally only sell out the entry level spec as they are most popular but i tend to go middle and up because i need the memory and never had a problem getting them.