I’ve had coconut milk kefir work very well, but as A_M says, it’s expensive. Also, you’ll need to refresh the grains in some sort of animal milk periodically to keep them from dying.
A_M, I’ve posted this elsewhere in the past, but this article written by a respected mycologist dissuaded me from drinking kombucha (which I made at home for years). If you don’t want to read the entire thing, use your browser’s “find” feature to skip to the mentions of its antibiotic nature. http://www.fungi.com/blog/items/kombucha-my-adventures-with-the-blob.html