I recently designed an adapter that allows you to connect a 15Pin PC Controller, analogue or digital, to the joy port of Amstrad CPC:
Adapter requires 5v supply, so i can provide an extra Y power cable too:
Apart from the required signal conversions, adapter is also equipped with a 3state buffer chip (74LS367) that isolate controller from Amstrad’s Joystick port, in order to avoid keyboard blocking!
It’s available for 12euros+shipping, anyone interested contact at: ikonsgr745@hotmail.com