USB Joystick Adapter from Retronic Design on Tindie
USBJoy2.0 - adapter. Connect your Atari Amiga C64 joystick to PC! Develop your own usb device! - Polish electronics for 3D printers, CNC, robotics, retro computers
Amazon.com: SPEEDLINK SL-650212-BKRD Competition PRO EXTRA USB Joystick - Anniversary Edition, Retro-Arcade-Stick, schwarz-rot : Video Games
UPDATE] Converting the “Competition Pro Extra USB” to C64/Amiga/Atari DB9 – pagetable.com
Amazon.com: Retro Games The C64 USB Joystick for PC : Video Games
Arduino Project: Commodore 64/Amiga, Atari 2600/XL/ST, ZX Spectrum Joystick to Windows/Linux (RetroPie) USB | jfrmilner's Tech Blog
How to Convert Any Commodore Joystick from 9-pin to USB using The C64 Joystick - YouTube
TheC64 Micro Switch Joystick
Resurrect your DB9 joystick, Mayflash USB Adapter Review – Vintage is The New Old