Most of the pumpkin farms at churches go up right around then. I'm also certain Walmart will have theirs by then too. Hope that helps!
This place starts their fall fest on September 17th, so they might have pumpkins then.
Also, Michael's already has their fake realistic pumpkins out too.
ETA: I think you might actually be a former client of mine based on your screenname--did I do your engagement photography early this year?