Here's an article about protein content of various flours.
Flour - Joyofbaking.com Apparently cake flour is similar to pastry flour, but not completely interchangeable. I know you can send to King Arthur for the flour, but maybe someone who's more knowledgeable can give you hints on how to substitute or mix various flours. I know you can get cake flour (Softasilk, Swan's Down) in boxes in many grocery stores.