That's Apple's job, not mine. The way people think Apple can walk on water, you'd think you could walk into one of their stores in their home country and buy their newest phone. But the iPhone is always in short supply for months, and the iPad mini was in short supply, and the Retina mini was in short supply, and if I recall correctly, the last redesign of the iMac was in short supply. I'm seeing a repeating pattern.
There are many more factors to weigh in here. Apple is making iPhones as fast as humanly possible. There is absolutely zero incentive for them to do anything else. Every single phone they make is already sold and money in their pocket. In addition, it is LEAN manufacturing supply chain genius. It is better for the company and better for the environment if they can produce product having a better idea of the demand in what amounts to real time. It is a responsible way to run a manufacturing business. No wasted resources, no massive inventory of unsold product.
The trend you are seeing is LEAN business processes at work. IIRC the shortages on the iMacs were almost exclusively with BTO models, which is reasonable at launch, especially if yields are not at optimal a levels for all components. Then all the other elements that go into managing supply chain, like component issues, issues with suppliers and manufacturing partners, etc.
This is Cook's strongest point, supply chain. If a side affect of that is an opportunity for marketing hype so be it. The other effect is you have to wait a couple of weeks for your gadget. Understandably frustrating, and understandably not in your personal best interests, but this is the way manufacturing should be run so it is most efficient.
The thing that makes it really difficult is that we are talking about unprecedented volumes never before seen in history, especially in the high tech advanced computer industry. There is no other company doing these levels of numbers.
If you want to complain about it, that's fine, but unless you have some good suggestions about how to make it better, then you should have some understanding about how difficult this is to pull off. And if you do have a solution that allows the company to maintain its process efficiency, maintain tight control of it's supply chain, and at the same time improve product availability for the end consumer at launch time, then Apple should hire you, you are the next Tim Cook.