These clips (white one pictured) do not appear to be available any more.

So I programmed the CAD up in OpenSCAD and printed them out. They seem to work nicely.

module rsquare(size, radius) {
 assert(radius < size.x / 2, "Radius must be less than half the width");
 assert(radius < size.y / 2, "Radius must be less than half the height");

 minkowski() {
   square([ size.x - radius * 2, size.y - radius * 2 ], center = false);
   circle(radius);
 }
}

$fn=60;

difference()
{
   
   union()
   {
       linear_extrude(1) rsquare([6.4,22.34],2);
       translate([0,0,1]) linear_extrude(2) rsquare([3.2,21.34],0.75);
       linear_extrude(1) translate([-9,0,0]) rsquare([15,6.4],2);
       translate([1.,1.7,0]) cylinder(6,6.4/2,6.4/2);
       translate([1.,1.7,0]) cylinder(8.4,2.1,2.1); // Connector    
       translate([1.,1.7,7.4]) cylinder(3,2.7,2); // Cap        
   }
   union()
   {
       translate([-2.2,2.25,5]) rotate([90,0,0]) linear_extrude(1.1) square([10,10]); // notch
   }
}