If you solder and are inclined to make one, its a pretty simple build. I needed some channel insert cables for a mixer, so I made some without a box-
One end has a 1/4" TRS (tip/ring/sleeve; aka "stereo") plug, and there are two cable whips coming out of this that terminate with 1/4" TS (tip/sleeve; aka "mono") plugs. The tip of the stereo plug goes to the tip of one of the mono plugs, ring of the stereo plug goes to tip of the other mono plug. Connect all plugs' sleeves together (ground), and voila. You could of course build it in a breakout box with jacks, etc... like the Ric units.
There's a diagram somewhere in the mixer's manual which I can find/post it if it helps anyone. That cable config works with my 4001 and former Mangum-1.