A survey of 60 Apple Stores by Piper Jaffray’s Gene Munster found that the iPhone 5s was in stock in all colors on all carriers and in all capacities across the US.
This suggests that if you’re in a hurry, a retail store is your best bet as some 5s models are still showing 5-7 day shipping on the online store. Online, all but a few models are showing immediate availability. It should be noted that with so many size/color/carrier combinations, smaller stores aren’t likely to have every one in stock.
Apple has been gradually catching up with demand for its high-end handset, with the gold model initially in particular short supply.