Overview
Design files:
I have zipped the Matrix button pannel v3.f3d, which is the Fusion 360 design archive file. This has my sketch, design, and all details which you can bend and use to your hearts content.
3D printed, it is a near perfect fit with the button pads and then securing screws for the neopixel trellis boards.
STL files:
8512.Matrix button pannel - frame edges.zip
Code (and libraries) Circuit Python:
In action: