Spotted this one on eBay, seems to match the lowest price listed previously - https://www.ozbargain.com.au/node/531346 - the model is a little old, but the reviews seem to be generally good, especially at the price. There were 10 in stock until I just bought one - so hopefully that counts for sufficient quantity!
From Sony’s Website ( https://store.sony.com.au/archived-wireless-speaker/SRSXB501... )
Thanks to EXTRA BASS™ and LIVE SOUND mode, the SRS-XB501G lets you feel and hear your music like you were there. And with the Google Assistant built-in, you can manage everyday tasks and play your favorite tunes without lifting a finger.
EXTRA BASS™ for deep, punchy sound
Google Assistant built in3
Fill your party space with LIVE SOUND
Up to 16 hours of battery life5(EXTRA BASS: Up to 12 hours6)
IP65 rated water-resistant and dustproof
Satellite Speaker(x2): 45 mm, Subwoofer: 4.92"
Approx.16 hours (Standard mode / Lighting off) Approx.12 hours (EXTRA BASS mode / Lighting on)
FREQUENCY TRANSMISSION RANGE
20 Hz-20,000 Hz (44.1 kHz sampling)