Coconut milk and coconut milk kefir are allowed on the strict diet. Coconut water is not, but coconut water kefir is fine (Able might disagree, I suppose, but I haven’t seen it yet).
Whole Foods’ store-brand organic canned coconut contains no extra ingredients and is $1.99/can. It’s the best deal for the best product, in my opinion. If finances aren’t a big issue, there’s a brand called Natural Value that carries additive-free organic coconut milk in a BPA-free can. It makes reeeeally good, creamy coconut kefir. Hands-down my favorite, though I’ve never seen it for less than $3/can.
I got my grains from a friend. A lot of people on here buy from the Kefir Lady website, though.