I don’t know, I would like to know if its possible to travel with them abroad also.
I used to live in US and my mom brought kefir grains to me from Bosnia. She was sneaky though, she put few little grains in a plastic medicine bottle. Nobody raised an eyebrow or asked what it was. Few little grains grew fast and we had a full cup of kefir within a weak or so. My parents traveled more than 24 hours so it took grains a day or so to restore their health.
There is a risk though. If they find it they will probably make trouble for you.