The resulting drink is sour and sweet, not unlike yoghurt. Enchanted I had my eyes on any of these vinegar culture on sale outside. On my last day luckily, I chanced upon Food section at Mitsukoshi at Ginza at B2. There brand is VISS 1882 launched by Japanese famous vinegar specialist, Imazuya. I was lucky too as the store was apparently the only one in Tokyo, and I found it by chance ;-)
There's interesting mixes available. The most popular one is Apple-mix, followed by Grape then Passion fruit.
Address:
VISS1882 銀座三越店 〒104-8212 東京都中央区銀座4-6-16銀座三越 地下2F