A collection of 3D files for the Monome Arc Clone by Johannes Neumann, which can be found at https://github.com/TheSlowGrowth/MonomeArcClone/
Knob - D-Shaft knob, fitment can be difficult based on the accuracy of your printer and material used.
Light Shaper - I've printed one of these but haven't tested fitment yet. You may need to use a raft to print successfully.
Case - I haven't tested this one yet, it is too large to print on my Ender 3. Update Printed on an Ender 5 Plus and made some small tweaks to improve fit. I use these on the bottom - https://www.amazon.com/Small-Clear-Round-Rubber-Feet/dp/B07C6R9SP8/