At the time of writing,the only charms you dont have to win or buy in a bank offer are Baggi charms.
Going on previous questions,and answers, Raine charms would seem to be the rarest listed in bank offers, but others, according to various factors, might not find this to be the case.
There is currently a competition running that gives some Raine charms as prizes, but they do not seem to award many, and unless things have changed recently, you only are eligable for the charms if you are NOT in the NOVICE league.
Its worth it in the long run to get Raine, but if you are not well advanced and in need of his attributes I wouldnt rush him.
In order to get to the next stage of any shaman you need enough charms to unlock it, but this number rises rapidly and the last stage alone needs 900,its a simple matter if you have enough, as the game indicates this with an arrow.