Cake flour usually doesn't come unbleached....bleaching makes it finer and softer...you might try www.kingarthurflour.com they are the only ones I know that carry unbleached cake flour. Here is the link:
Just keep in mind that the texture of your cakes wont be as fine or soft because bleaching makes the flour white and finer or silkier....you can try sifting it a few times which will help alleviate this issue a little...