I bought a RGB trackball for my CP
Cowboy Arcade Project because I wanted my trackball to light up orange to match everything else. The problem with this is that when it is not lit it will be milky white which I really don't like. Also, I plan to light the controls for the game in use, so this impacts the look even when the cab is in play.
I started looking around for a replacement ball that was clear orange (so it would look good unlit and lit) and none of the arcade parts suppliers had anything. So I switched to looking for translucent 3" orange acrylic or polycarbonate balls and guess what I found....
Juggling balls!
There are lots of suppliers I am sure, but there are also lots of sizes. You need a 76mm acrylic ball. Like the orange one I just got in the mail!

Turns out that 76mm is almost exactly 3".
Here is the place I found mine:
Fire Mecca. I don't have any connection to this company at all, just bought from them and am very happy with the product and service.