Let me amend my previous statement: Don't ask, LOOK. If it ain't on the shelves, they don't have it.

If you're feeling particularly masochistic, and feel you MUST ask an employee, even though you've been up and down the roofing aisle a dozen times and all they have is aluminum or round vinyl, call it "downspout" and see what happens. "Gutterpipe" is not the technical term.

One store chain I KNOW stocks square vinyl downspout is Chase-Pitkin in the Western and Central New York area.