Hi,
In fact shoofly pie isn't really a pie. It is a cake with a crumb top, which happens to be baked in a pie pan.
The origins of the name suggest Shoofly is a poor transliteration of the french work chou-fleur, which is cauliflower. It has been suggested a shoofly pie looks like a cauliflower.
Recipes are all over the place. I agree with Josephine this should not be too difficult to make at home. Believe me, if I knew where you could buy it, then I would advise but no place comes to mind.
Regards,