National retailers here do weekly flyers by state - usually one each for regional and metropolitan area stores per state. As long as they haven’t overextended locations beyond that which they can reliably supply to, it’s really not hard to ensure availability for a product before you put it on sale, or vary the sale conditions according to availability in a way that’s totally fair to consumers.

In areas too remote for reliable supply to a national chain location, e.g. remote Western Australia, you just have co-operative independent retailers with their own prices. There needs to be a certain level of suburbia before a national retailer location becomes viable