Findmall, here, etc., all list advertised upcoming hunts that people post about. Western & Eastern Treasures magazine publishes a list of open hunts they know about months in advance in every issue. There's hunts all across the U.S., just depends how much you want to travel.
Ones I know of near you coming up you may want to check out:
July 12-19, Stanton, PA - Treasure Week 2013 @ Fox Den Acres Capmground in New Stanton. 8 days, 2 miles from the PA turnpike & I-70, 3 daily hunts, sponsored by manufacturers / clubs.
Sept. 21-22, Java Center, NY - 15th Annual International Hunt sponsored by Genesee Valley Treasure Seekers @ Beaver Meadows Campgrounds. gvts.org
Oct 5-6, Washingtonville, PA - 33rd Annual Treasure Hunt sponsored by The Susquehanna Valley Metal Detecting Club and Tesoro held at the Montour-Delong Fairgrounds. 3 hunts each day.
http://www.losttreasure.com/calendar-date/