I have a variety of Avocet spare parts from the Avocet 30, 35, and 40 series. What model cyclometer do you have? I only ask because all the cables I have come across have been grey, although some of the brackets are black (but usually grey also). The black brackets that I have attach to the front of the fork blade, while the grey ones push over the top of the dropout - both types being secured by zip tie(s). I also have pick-up rings in both black and grey. And several working cyclometers in various colours.
I'm a newbie on here (although I have sold a lot of retro bike bits elsewhere). I'll try to post photos of my Avocet stock here in the next couple of days. That might help pinpoint if I have what you need.