Preview images? What preview images? Oh, those ones. Yeah, we've got those. Check out the direct links for each Android N preview image download below (all devices shown except the General Mobile 4G, which will get images at a later date).
The Android system images are previews and are subject to change. Your use of the system images is governed by the Android SDK Preview License Agreement. The Android preview system images are not stable releases, and may contain errors and defects that can result in damage to your computer systems, devices, and data. The preview Android system images are not subject to the same testing as the factory OS and can cause your phone and installed services and applications to stop working.
: If you manually install a preview system image on a device, that device will not receive additional over-the-air updates (either production or preview). If you want to update a device with a new preview system image, you must perform another manual installation.