There’s tons
You don’t have to join one. You can.
I’ve been pondering over it for ages and considered many… there’s a free one I think called Quararia or something that’s online if you just wanna have a look and see
I don’t think all are equal in what they offer or teach or in their reputation so I would recommend asking people for their experience or thoughts here if you find one you resonate with
Also just noticed this post which may be an interesting read for you CKs black magician beginner guide