See
http://www.manfrotto.com.au/
Though Manfrotto mounts are ubiquitous in camera stores, certainly here in
Sydney, chances are they won't stock a 161MK2B, so you might like to
email
info@manfrotto.com.au to find a suggestion for a dealer who might order
one in for you. For example, this online store -
http://www.camera-warehouse.com.au/p/manfrotto-161mk2b