I do a lot on the 3d printer. I've done a bunch of audio related things and was considering doing knobs as well. 3d print is never going to look exactly like a molded or milled/painted piece. That being said for proto purposes is amazing. You can then take your stl file and have a shop produce them.
Reason for posting, if anyone wants to dabble, tinkercad.com you can design your own stuff and output an stl file. No cost and you can get some pretty crazy stuff done with the limitations of the service.