Design your own custom knobs!
Many different kinds are possible.
Open in Customizer or OpenSCAD. The OpenSCAD script contains some additional settings for advanced users.
Depending on the design of your knob and your printer, you may need to turn on support material and/or flip the knob upside-down before printing.
If you use the "recessed" cap type, your knob will have a divot at the top which you can paint with enamel paint if you wish. If you have several knobs on a device you could distinguish them by the color of this paint.
Depending on your printer, you may need to make holes 0.5mm or so larger than necessary (though you probably know your printer better than I do).