Sound board PCBs and finished kits can be ordered here: EZ Soundboard (fortner.industries)
All files are designed to print without supports. The box should be printed with the open side facing up. The model in the photo is Polymaker Tough PLA printed at .200mm and 30% infill.
The brass inserts M3 x 3mm x 5mm.
The black screws are M3 x 8mm flat head.
Two lid options are offered: a base flat version, or one with a GoPro mount.
The jig part is optional, and only helpful if soldering the PCB components yourself. It helps align the keys while soldering, but isn't required for the case.
The author hasn't provided the model origin yet.