Carol, here is a reliable site for ordering kefir grains or powdered starter...
I've never seen the grains at a health food store, but I know Whole Foods carries the powder. The powder does not have the multitude of probiotics that the "real" stuff does, but is still good.
I don't know where you live, but if you find a source for raw cow or goat milk you may find people that will give you some. That's how I got mine!