There are anecdotes of people walking in and getting them.

There are a couple of services which scrape apple.com and look for stock and notify you.

I registered with istocknow.com but haven't gotten any notice of any availability.

They do show overall 6 and 6 Plus availability. 6 has greater availability.

But they're trying to roll out to China and aggressively launch in other countries. So maybe the US isn't getting as much supply. Though stores have display models ...