I don't know about the English Mark Darts, but on the Pub Time Darts, the monitor just takes composite video. For a while I was using a little 9" security monitor until I got around to fixing the original one.
I actually just found a 9" CRT made by the same company on Ebay. It's a green monochrome not amber, but it looks like the screen has absolutely no burn-in.
You can feed the video signal from the dart gameboard's RCA "video out" jack to any tv set that accepts standard NTSC composite video. Yes, many B&W security camera system monitors will work.