Target lists November 21st for iPad mini Retina release1
The best thing to do if you're unsure there will be enough supply is to delay the release as long as possible. If Target is to be believed, that's exactly what Apple may be doing. The Target product page is putting the release date for the iPad mini Retina at November 21st, which would be just one week before Thanksgiving, and therefore just eight days before Black Friday.
Given that Black Friday is often the second biggest shopping day of the entire year, Apple has to have the iPad mini on store shelves before then, but it's unclear how long the supplies will last after that.