@kitkatb Kombucha is available in the shops, pretty much everywhere in Melbourne anyway! I like the Remedy brand but there are so many, you just have to keep trying them until you find the ones you like. I have been drinking them for years now and have never had an infection. I always notice an improvement in my gut situation when I drink it regularly.
A few weeks ago I did a fermentation worshop and am now making my own kombucha, scoby and all!
I'm also making my own kefir. I was very suss on it at first, because I'd only tried one from the supermarket once and I hadn't liked it. But the homemade one is gooooood! I like to put a pinch of cinnamon and a bit of honey in it. I can see no reason why you couldn't add it to banana to make a smoothie!
So kefir, same as kombucha, keep trying until you find one you like. You could try health food shops too.