When Apple introduces a new colour to the line up they normally get back ordered pretty quickly. With the iPhone 7 comes jet black and black, two new colours that look great. I was never into rose gold or the standard gold but with these two new darker ones I'm interested in trying them out.
As you know if you are reading this the Jet Black model is already back ordered to November and the most obvious way to order one is to get in line and wait a couple of months but there is another way.
The way that this has worked out for me in the past with high demand Apple devices is to first off make sure you install the iOS Apple Store app (you can do this in Safari but I'd recommend using the app for speed).
Make sure you favourite your designed model then check for Pickup rather than delivery, this method has gotten me all of the in demand products I've been after in the last few years. Check daily and when your local stores get stock make sure you reserve for collection.
Last year with the 6S when it went out of stock online the in store pickup system was updating daily and although the demand wasn't as high as this seems to be it got me one on launch.