<<Disclaimer: Verify this information before applying it to your situation.>>

In the "Old Farmer's 1997 Almanac--Special Reference Edition" is a
chart of substitutions for common kitchen ingredients, including
different flours. This might be helpful in a pinch if you don't have
what you need to mix up a batch of gf all-purpose flour, although the
results might not be quite the same, of course, if all you had was
cornmeal or potato starch.

Bobbi in Baltimore