I've made my own monitor cables in the past. It's not hard. Three wires for RGB and three for their grounds at the Amiga end (the grounds can all go to one pin at the monitor end), and then a composite X-Y sync wire with a ground.
That's it - eight soldered connections inside the 23-way Amiga plug. At the monitor end, I have used DIN plug (old Commodore monitor) and BNC connectors (PC multiscan).
