Organic restaurants in Austin, TX
I've seen kefir for sale at the downtown farmer's market. I do not know if it was organic, but I'd sure hope so for the price he was charging ($8 or $9 if I recall correctly for a quart). You can also find organic kefir at Whole Foods, Central Market, and HEB (Nancy's is the brand I think).
I've never been to Casa De Luz but have heard from others that it's good. In addition to being organic, it is also vegan and macrobiotic.
There are a ton of other restaurants that have organic items on the menu, but except for Casa De Luz, I can't think of any that advertise as 100% organic. One of my favorites that serves some organic items and has a garden and chickens on the property is The Eastside Cafe.
I've enjoyed the avocado and veggie "chorizo" tacos, among other dishes, at the Daily Juice Cafe, which is organic, raw, vegan, and gluten-free. Their desserts are also surprisingly yummy.
We've also got Borboleta (organic, vegan, gluten-free, not raw) and Beets (uses organic & local ingredients where possible), which I haven't tried.
TerraBurger is a local burger place that uses organic "core ingredients".
I'd also recommend Casa da Luz. Another place that serves local and organic food is Somnio's though i've never been. It's on S. 1st.
As verily said, you can easily find organic kefir at most grocery stores. I've purchased it from HEB, Central Market, and Whole Foods. I'm not sure i've seen it at any of the farmer's markets but i wouldn't be surprised.