Pop'n Bounce uses a spinner, not a trackball.
You can get a board to make one here:
https://nhb-shop.com/products/ng-spinner-controller-board-for-neo-geo-mvs-aes-cd
You can get a board to make one here:
https://nhb-shop.com/products/ng-spinner-controller-board-for-neo-geo-mvs-aes-cd