Oh, you don't have to use raw milk. That's just what these kefir grains were initially grown in. You can use any kind of milk: cows milk, goat's milk, or even coconut milk. I use organic pasteurized cow's milk. At first I used "ultra-pasteurized" by accident and the kefir grains weren't adapting to that milk very well. I found out that "ultra-pasteurized" means it is highly processed and doesn't have a lot of nutrients or food for the kefir to live off of.
Any of the milks you use can either be organic or not, depending on preference or availability. I haven't tried coconut yet.
I think a lot of the kefir grains on ebay sounded like good ones. If you want you could check out the other listings too. I just based my purchase on how many good reviews the seller had - but I bet there are a lot of great sellers. Good luck!