KensingtonWorks Button4 & 5 (like old TrackballWorks) : r/Trackballs
Kensington SlimBlade Pro Bluetooth Wireless Rechargable Ergonomic Trackball Mouse for Windows and macOS, Ambidextrous Design and Optical Tracking (K72080WW) : Amazon.co.uk: Computers & Accessories
Kensington Trackball Mouse - Orbit Mobile Wireless Mobile Ergonomic TrackBall Mouse with Touch Scrolling, Ambidextrous Design and Optical Tracking - Certified to Work with Chromebook (K77600WW) : Amazon.co.uk: Computers & Accessories