I tracked these down. We got more in at my feed store, so I was careful to check out which box they were actually in. They came from a farm known as Fifth Day Farm aka Blue Banty Farm, the info for which can be found on the Freedom Ranger Hatchery Website.
So I called them. These are indeed a silkie hybrid, though that's about all the person I talked to really knew about them. Based on what breeds this conglomeration of farms seems to work with, I'd bet they're a silkie/freedom ranger hybrid or perhaps a cross between silkies and the hybrid they are calling 'rustic ramblers', which might explain the 'Southern Rambler' breed name.