This recommendation had more information than any others, including a parts list. 

https://www.amazon.com/dp/B07TLK4956

The teflon sliders are super expensive.  Would try using teflon sheets & double sided tape. 

https://www.amazon.com/KAILH-Official-Chocolate-Mechanical-Keyboard/dp/B0B3MLZJ8K

 He had good results using mechanical keyboard keys for buttons but they're super expensive. 

Just the teflon & the buttons would burn $30.  The mane difficulty was the scroll wheel.  The best he could do was put it on the side.  He used a clickless encoder.

The problem is so hard, the lion kingdom started pondering trackballs again.  The scroll wheel is really hard.  It would ideally be a mechanical keyboard key with a wheel.