I haven't seen it advertised anywhere, but I was checking out the Masters website and it looks like the Adelaide Airport store will open on Wednesday.
https://www.masters.com.au/Stores/SA-OPENING-DEC-Adelaide-Ai…
Not sure what Masters normally do when opening up in a region (Mt Gambier doesn't count), but hopefully there are some good opening deals.
They generally hand out coupons to all guests on the first day, which entitle you to purchase 1 item at 10% or 2 items at 15% and 3 or more items at 20% off list price. It's quite good if you need a few expensive items, I stacked mine with a BBQ and 2 air conditioners, another time 3 wall hung vanities, and lastly a BBQ, pressure cleaner & hammer drill. Lucky I had 3 Masters open nearby
(I'm not associated with masters either, regardless what the tag says)