We have had some 3m extension cables made up to fit our MON705 and MON7005 monitors. These are useful if you wish to mount the monitor above the windscreen but keep the power supply and camera leads in the dash area. To our knowledge we are the only supplier of these cables in the UK.
The 13 pin connector is quite commonly used. These cables can be used on other manufacturers monitors, but the video may be on different pins. This might lead to some minor image issues.