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It's on Azon.
That said, any coarse ground will work and - truth be told - even cheapies, as there is no heat to draw out the bitterness. I'd never cold brew expensive coffee, for example.
Personally, I use store brand ground. put it in a quart jar, + let it sit 12-18 hours in the fridge. Never going to win any awards, but provides the necessary caffeine fix on those days when I don't expect to be able to fire up the Keurig, boil water for the AeroPress, etc.