You can order a ploopy[0] kit or modify their source[1]. I think a few users on r/trackballs[2] might have gotten QMK to work with it.

[0] https://www.ploopy.co/

[1] https://github.com/ploopyco/mouse

[2] https://www.reddit.com/r/Trackballs/comments/dk4ha7/ploopy_v...