You can now preorder the Nikon Keymission 360, directly from Nikon. If you order before October 22, 2016, you will get a free KeyMission Accessory Pack that includes a tripod, extension arm (handle / selfie stick), carrying case, and rechargeable battery. Here is the link!
Also available from B&H with free 2-day shipping (double-check if free shipping is available where you live) and from Amazon with Free Prime shipping. Depending on where you live, you might not need to pay a sales tax with one or the other. I've confirmed with B&H that if you order with them, you'll receive the free accessory pack as well.
At $499, the Keymission 360 is more expensive than the Samsung Gear 360. However, if you include the value of the Accessory Pack, it decreases the effective cost.