Here's what The Cook's Thesaurus has to say:
cake flour = soft-wheat flour Equivalents: 4 1/2 cups cake flour = 1 pound Includes: self-rising cake flour Substitutes: pastry flour (This has more protein than cake flour but less than all-purpose flour. Cakes made with pastry flour tend to be a bit less delicate and crumbly.) OR all purpose flour (Substitute 7/8 cup all-purpose flour for each cup of cake flour and add 2 tablespoons of cornstarch for every 7/8 cup all-purpose flour used. Cakes made with all purpose flour tend to be less delicate and crumbly.) Hints: These substitutions will perform better if you also do this: (1) Mix the batter as little as possible. (2) Separate eggs, beat the whites, and fold them into the batter
One note about substituting: Make sure you don't forget the cornstarch! I made the BA Lemonade Cake for Easter last Saturday and didn't have any cake flour. When I started to turn the cake over to cool I noticed it started sliding. I really didn't want to turn it over, but my mom said - "That's what the recipe says, you're supposed to cool angel food cakes that way." When I did the entire cake fell out of the pan - part on the counter, part on the floor. We were laughing hysterically. Then I remembered I forgot the cornstarch. I'm not sure if this is why it fell or some other reason, but just wanted to forewarn you. (BTW, the cake tasted delicious, even though it was just a huge blob on a plate. Needless to say it didn't make it to the Easter table. )
Life is either a daring adventure, or nothing. To keep our faces toward change and behave like free spirits in the presence of fate is strength undefeatable.