hi
i never liked pc joysticks. the ones which look like a real joystick are not "clicky". it is a nice thing that they can sense when you only turn them a little, but this is not required for boulder dash or any other c64 game. gamepads are also useless (to me), once i could not find any, on which the direction buttons are on the right (!).
so i did the following. i bought the cheapest gamepad i found. (notice: the direction buttons are on the left hand side

)
i disassembled it, and did a bit of soldering work. i drilled a hole to the back of it, where i mounted a male dsub-9 connector, and wired it so a c64 joystick can be plugged into it:

it was fairly easy to do, just had to see which wire goes to which button.
so now i have a real c64 joystick with an usb interface

i also use it sometimes to play gdash.