To date there are still only a couple of single handed pistol grip styled 3 Axis Gimbal Stabilizers designed to support cameras like the Panasonic GH4, Sony A7s, or even Canon T4i. The first ever and possibly still most popular one available is the Nebula 4000 from Filmpower. Here's a quick interview from the Camera Motion Research booth during our NAB 2015 coverage.
Although the Filmpower Nebula 4000 Gimbal can be found around the world, USA residents should visit Camera Motion Research. They may be the only USA reseller of the Nebula 4000 gimbal. You'll benefit from their fast shipping, quality customer support, and domestic shipping if you ever have to deal with warranty issues. Even if you have just basic questions about the Nebula 4000, you can contact Camera Motion Research over at their website http://camotionllc.com (found here).