We've just been tipped off this evening to a Best Buy location that's been scheduled to have a mysterious "Apple fixture" installed on Friday, October 21st. That lines up nicely with some of the most recent iPhone 5 rumors pointing to a mid-October release, and considering that we're already in September and we don't have a press event on the books yet, October availability is looking more likely by the day.

To be clear, this isn't a run-of-the-mill installation for the big box -- our tipster tells us that the request that a manager be on-hand at 6AM is out of the ordinary (they usually show up at 7AM for inventory), and that a similar arrangement was scheduled for the iPhone 4 launch. While it seems strange that thousands of retail employees could potentially be clued into iPhone availability over six weeks in advance, the language in Best Buy's system is sufficiently vague so that it could technically be anything. It's just hard to ignore the correlation to the mid-October rumors, particularly when the Wall Street Journal's throwing its weight behind them.

On a related note, our tipster tells us that Best Buy Mobile managers have a meeting scheduled for October 10th to "discuss upcoming BIG release dates" (emphasis his). Assuming we get an Apple press event for the new iPhone a few weeks in advance, the managers would be well aware of the release date in time to discuss it at that meeting, so that'd support a release on or around the 21st, too.

We'll pass on more as we get it -- and in the meantime, it couldn't hurt to mark this one down as a date to watch in your calendar.