Drums are still widely used throughout the north-west - not just mining exploration but cattle stations also. Fuel in drums is mostly Jet (which lasts longer in the heat) but Avgas is available also, given plenty of notice. The main supplier of Avgas out there would be Recharge :
https://www.rechargepetroleum.com.au/replenish
I'm not sure what it's like there now, but +20 years ago when the Casino was in full operation, the only way to get fuel to Christmas Island (there being no place for a ship to dock in rough weather) was to drop the drums overboard and tow them into the beach by dinghy!