You can get something similar here, it's not exactly kefir, but it's a kind of soured/fermented milk product, but runnier than yoghurt.
It's sold as Active Lactic Culture and the packages looks something like this depending on the brand.
Expect to pay about NT$250 for a pack of 10 sachets which each makes 1l of the stuff. You'll find it in the refrigerator in most health food shops here. You can usually make a few more batches from what you made from the sachets, but it doesn't seem to go on forever. Also, it's done in room temperature, but it doesn't seem to be happy if it's too hot or too cold. I couldn't make it set here in the winter and I've had problems in the summer sometimes.