Could be store-specific but found these in a box on a pallet near the timber yard entrance at Bunnings Waurn Ponds.
More than 10 left by the time I left at around 11:30am. The blue and yellow ones seem heavy duty to me as the wires look to be a bit thicker. There are also some 15m ones mixed with the 20m ones.
I picked up two 20m ones but they were still scanned $25 at checkout so make sure to ask the staff members to change the price.
Good Luck!
Seven Hills bunnings had these last week as well - so did Castle Hill - so I assume its nationwide clearance?