I know Michaels puts all their Halloween stuff out before the end of July, and they usually put general fall decor (including some Gemmy foam pumpkins) on display even sooner. Won't be long now. We'll all have to keep our eyes open and report out sightings.
More history: Check out
this thread from a couple years ago. pagemaster1993 reported that some pumpkins were coming out by July 6. And snow2alike saw some fall products a couple weeks earlier.