A Ploopy is a brand which sells Open, high-quality pointing devices. Website 
Mods
Because the designs are open, there's a community of modders that modify and publish designs. That's part of the appeal, the base product is high quality but it's a lot of fun to tinker.
The Verge has a great post titled "My rapid descent into the world of DIY trackballs". Article
Ball Transfer Unit cutaway. Source
There's a BTU mod for the Ploopy which makes the roll virtually frictionless. Github
Sourcing BTUs might be best from McMaster, it just works. Website
Adam says there are a few SKU suppliers that would be good. BTU Spec Sheets
Mystery: BTU mod page claims newer ploopys come with a 45mm ball. However, this is smaller than the smallest size. Ball Dimensions
YOUTUBE 8cu-j3vi-RM
BTU Mod for Ploopy Classic Trackball. Source
It looks like you can buy hollow brass balls which might work inside ploopy. Shop
Smooth finish with Acetone. Reddit
Maintenance
Polish the pool ball with a cleaner designed for it. Aramith Ball Cleaner
Restoring shine on Billiard Balls. Article