National is not yet offering it for Oct, only short-range bookings a few days ahead of time in Sept. Same for Alamo and Enterprise. I suspect this will change eventually, but I wouldn't plan on it.
It was the same thing that happened with the FL driveout last year. Enterprise and Alamo were consistently offering the promotion. National usually did not, but when it did, it only jumped in for a handful of days, and mostly at the last minute.
My recommendation would be if those are the dates you must use, book with somebody else on Autoslash for now, to make sure you get a special rate. The promotion can be withdrawn at any time without warning. Then, Autoslash will email you if prices drop with anybody. I suspect they will. And you can keep checking with National to see if they decide to slowly open availability for the special.