There is Cholov Yisroel kefir from Wayside Acres with a Lakewood hechsher. The grains I’m afraid are only available in Eretz Yisroel, unless someone snuck some out, or the manufacturer here is willing to share. But I could be wrong so ask around.
It’s also good to know that you can actually “produce” kefir by mixing some kefir with regular milk, cover with breathable fabric/paper and leaving at room temperature for about 24 hours — and it actually works for about 2 or 3 times. Big money saver.