This article explains how to convert a “Competition Pro Extra USB” (which you can still buy new) to work with a C64, Amiga or Atari. For the conversion, you need a joystick extension cable like this:
I have a huge amount of them, with the wire colors described in the article, and I am happy to mail one (or more) to you for free within Europe. Reach out to mist64@mac.com/@pagetable.