I heard from other BK mum said : Mommymart 腰包型揹蔕 available in Seiyu Shatin Dept. you may give the dept.store a call b4 going.price around $450-600 not sure the recent price. Mine was bought 1.5 years before cost $5xx from former bb dream.
Aprica and Combi should available in Wing On and Ho fa and BB dream.
I saw Aprica 揹帶 in Seiyu and BeBe Dream, not out of stock wor, many stock wor. The sales there explained to me about the usage, very good wor. Aprica got 3 ways and 4 ways 揹帶. And the price is only 3/4 of 荷花。