Where to get active Milk kefir grains
Sorry, I didn't see this until just now. I don't know why it didn't notify me.

Kefir grains are a life symbiotic culture of bacteria and yeast. They have to be fed and I imagine it is a niche market. Kind of like sourdough starter in that regard. I'm not surprised you didn't find them in a store.

People who have grains regularly have extras to dispose of and I have found they are usually eager to share and get other people hooked.

The last time I found grains it was on a forum dedicated to that purpose. I picked them up in a different state as I was passing through. Unfortunately this was about 10 years ago.

A quick Google search for kefir grains sharing sources turns up many resources. I will second ecnerwal that Craigslist is a good place to start. Freecycle is a good candidate.
I ran across this page that refers to a Facebook group.
http://www.yummykefir.com/get-milk-water-kefir-grains

I'll be surprised if you don't easily find grains in Austin. For better or worse kefir has kind of become a hipster probiotic thing.