SmallRig has its L-Bracket and Cage for GFX100 up for pre-order with launch discounts on their website. You can pre-order the L-Plate here and Cage here. They also have accessories available on B&H Photo.
SmallRig L-Bracket for FUJIFILM GFX 100 APL2349
Key Features:
1.Designed for FUJIFILM GFX 100 Camera
2.Arca-Type Plate with Center Marks on Both Axis
3.Built-in Flat Screw Driver
4.1/4”-20 Accessory Threads & Integrated Slots for Carry Strap
5.Features 1/4 Threads in front for 15mm Rod for Follow Focus
SmallRig Cage for Fujifilm GFX 100 CCF2370
Key Features:
1. Form-Fitted Full Cage for Fujifilm GFX 100
2. 1/4″-20 & 3/8″-16 & Arri locating Accessory Threads
3. Integrated Cold Shoe and Strap Slots
4. Secures to Bottom of Camera and use a m2.5 Screw on the Side to Re-tighten
5. Built-in Flat Screw Driver on the Bottom
6. Optional HDMI Cable Clamp1693 and Dual Rod Clamp 1943