You can make your own, or you can buy them online! My friend Amanda sells hers dried if you are in the States, or often you can go to a bakery and ask if they will give you some of theirs. If you have any friends who bake sourdough you can ask them for some too - you only need a tiny bit to start off, and you can then feed it for a bit until it is healthy and ready to go. You can't adapt this recipe to not use a starter, so make sure you have one ready to go before starting.