Thanks for pointing out those other kits. I have found several parts on thingiverse that people have created to add switches as well.
The Shapeoko 3 itself is opensource under creative commons, and it has a stock end stop switch kit which I presume is open source as it’s being sold with the machine by Carbide3D. So the files for those plates is what I am after, but I cannot find them.
From the Wiki: (https://www.shapeoko.com/wiki/index.php/About)
Goal: ShapeOko’s goal is to design and build a fully open source (open hardware) 3 axis CNC machine that anyone can build for the lowest possible initial cost.
That would indicate that the standard end stop kit should be open source, but I cannot find anything about the brackets. The section about adding the limit switches (which will soon be required) just points to the installation manual/documents, but no part files.