As horrible as it is to say guys, we all know that the 256GB models are the most popular due to the polls done here on MR. We also know that the silver is more popular than the space gray. (so, the 64GB space grey was only liked by about 16% of people).
By all appearances, the Carriers, Best Buy, Walmart and Target (in the US) were seeded in advance - I'd offer that the stock for the stores was as well.
The US is Apple's favourite child. They have many, many more opportunities to get what they want.
We really should expect the stock at the stores to be the luck of the draw. Many will be disappointed. But, DO keep to your heart's desire - appears more shipments are in the offing....delays aren't what was slated.
If you don't see what you seek, best you await a better opportunity.
(and, yes, I've been drinking....makes the wait FAR more tolerable!!!)

Cheers!
Happy hunting everyone!!!!