There are covertors for digital joysticks to use the 15 pin analogue PC joystick port, though I doubt they enable all the buttons on CD32 pads.
There are some good joypads for PC too, my son uses a Gravis one thats the same layout as the original playstation pad, including the 4 shoulder buttons. I've got a couple, it has to be said the Microshaft Freestyle Pro is fun, where it has tilt sensors and you move it instead of using a D pad - probably the best thing they ever made, lol :-)
