At Camerasize you can compare the A7c with all other cameras. And this is the size comparison between the SonyA7III and the new SonyA7c by Apotelyt:
Preorders:
In the USA at BHphoto, Adorama, Amazon, FocusCamera.
In Europe at Calumet DE. Foto-erhardt DE. Fotokoch DE. Wex UK. Park UK.
Sony HVL-F28RM External Flash at BHphoto.