Useful info, no doubt, but I think there have been reports of this for nearly two weeks now- though still no official announcement has been made (to my knowledge), as I still don't think all bands are available in stores, and inventory levels are not consistent.
I went to an Apple Store last week (5/22 I believe, as my Black Sports Band was set to [and did] deliver on Saturday 5/23) after many people had been sighting bands in-stores to check out what they had. They did have many Sport Band options on the shelves towards the back. All but the pink, I believe was available and if I remember correctly they had them all in both 42 and 38 sizing.
Having my original band being a blue sport band, and knowing my black sport band would be delivering the next day, I wasn't looking for another sports band at the time. In fact it was my first time seeing any other bands in person, as I had pre-ordered my watch without ever having a sizing appointment or even stepping into an Apple Store. Prior to that, I was going into the store with the mind-set that the Classic Buckle was the only other band I wanted at the time- I close to hated the Milanese Loop from pictures, and disliked the Leather Loop as well. Both of those changed however upon seeing them in person. So much so that I was now considering all three of those as my next band.
Anyways, I thought the Sports Bands on the shelves may be all they had, but after speaking with an employee, I was told they had more in the back that they'd received recently, and that shipments had been bringing in random quantities of bands of late. He said he thought he'd seen some Milanese loops come in, though after checking the back, they were gone (and my guess was they may have been for the 38, I have a 42). And I ended up walking out after purchasing a Classic Buckle, which I absolutely love and am wearing right now.