Wholesale distributor Video Products Distributors is listing a Harvest Moon: The Lost Vall due out for 3DS in North America on October 7.
A Harvest Moon of that name has not been announced, but this is likely the U.S. localization of Harvest Moon: Tsunagaru Shin Tenchi (Connecting the New World).
Unfortunately, access to VPD’s listings are restricted to registered members of the website. For now, GoNintendo has a screen cap, if you want to check it out.
Also worth noting, the same website lists Super Smash Bros. for Nintendo 3DS as an August 26 release. And it has Cooking Mama 5: Bon Appetit, whose localization is still unannounced, listed for October 14.