Where can I buy a fresh pumpkin out of season?

I want to home brew a pumpkin ale for Halloween. It takes about one full month to brew, and I'd like to do one practice attempt first, so that means I need to obtain a pumpkin now even though Halloween is about two months away. I know that some recipes do not require actual pumpkin, but the one I want to use does. Also, canned pumpkin will not work. I want to somehow obtain a fresh whole pumpkin in late August/Early September.