Pastry flour is flour with a much lower gluten content than regular
flour. If you cannot find it then you can approximate it by the following:

If you have a scale then combine 2 parts all purpose flour to one part cake
flour by weight (2/3 all purpose flour, 1/3 cake flour).

If you do not have a scale and want to go by volume then combine 4 cups of
all purpose flour with 2 1/4 cups cake flour. Fluff your flour (stir it
around to loosen it up)prior to measuring and sweep across the top of the
cup measure for accuracy.