Camera Foundry launched their CineBack rig for both Sony FX3 and FX30, which are practically the same camera regarding build and ergonomics. The new CineBack features top and bottom plates and quad D-Tap outputs straight out of a V-mount battery. As of the time of writing the first three batches are already sold out.
Source: https://www.cined.com/camera-foundry-cineback-for-sony-fx3-and-fx30-launched/