Yes, there is a 120 film camera that shoots 6x3. The camera in question is the Horseman 6x9 Roll Film Back for 6x12 Cameras, which is designed to fit on 6x12 cameras such as the Horseman VH-R and the Horseman VH.
The Horseman 6x9 Roll Film Back has a built-in film mask that allows for shooting in 6x3 format. This format is achieved by exposing half of the 6x9 frame with each shot, resulting in two images on a single 6x9 negative. The resulting images have a 3:1 aspect ratio and measure approximately 56mm x 168mm.
The Horseman 6x9 Roll Film Back is a versatile accessory that allows photographers to shoot in multiple formats without the need for multiple cameras. In addition to the 6x3 format, it also supports standard 6x9, 6x8, and 6x7 formats. The back is easy to install and remove, making it a convenient option for photographers who want to switch between formats quickly.
The Horseman 6x9 Roll Film Back is a reliable and durable accessory that is popular among film photographers. It has been in production for many years and is readily available on the used market. The back is compatible with a wide range of lenses and cameras, making it a versatile option for photographers who shoot with medium format film.