Can all-purpose flour be used instead of cake flour?

I wouldn't recommend using all-purpose flour instead of cake flour – they have different levels of protein which impacts cake texture. You can try AntoniaJames' recommendation if you definitely can't get ahold of cake flour, but using real cake flour is definitely the best way to go (in recipes that call for it) when possible!

The time-honored substitution for cake flour - one which will work here -- is for each cup of flour called for in the recipe, measure and level off the all-purpose flour into a one-cup dry measuring cup (or weigh the flour, if using mass measures) and then remove 2 level tablespoons of the flour. Put the remaining flour in a small bowl and add two level tablespoons of cornstarch. Whisk well to blend. ;o)

P.S. I don't know if it's possible to get cake flour in smaller amounts, except perhaps if your local bulk food store sells it. I've only seen the large boxes, throughout the many decades I've been baking.