This varies based on location, but most Apple stores around me (north NJ) show many models in stock, some 6+ too but mostly 16GB. Is Apple hoarding all the phones to themselves? Who knows but probably. On my second line, I got approval for a super early full discounted upgrade (upgraded to 5s last October!), but I can only order it through the retention department yesterday. I was quoted 30 days shipping on the regular 6 space gray 16GB. That phone is available at every Apple store around me, including stores in NYC. They quoted 10 days for gold and silver. It was a surprise that gray has such a long delay with AT&T.
PS, unless you have a good reason to buy from Best Buy (I did, because I signed up for the free $50 giftcard earlier this year), the Apple store will probably get you out much faster. I was one guy ahead of me yesterday at Best Buy and I waited almost 1 HOUR. Both guys were doing trade ins, picking out accessories, having geek squad backup and transfer their stuff, had to deactivated find my iphone on their trade in, one even had them install their screen protector

It was not worth that $50...