Found this one quite by accident! Wide open availability from DAL (Dallas Love Field) to Istanbul, Turkey (IST) on SkyTeam: Delta, KLM, Air France. Wide open for most of 2016. I was unable replicate from other departure cities within a few sample searches.
BOOK ASAP! You can always purchase on Delta and cancel within 24 hours.
Samples Dates are departing on Mar 16, 2016 and returning on Mar 23, 2015. Search on Google Flights and book through Delta or Air France.