These are often found on vacuum cleaner cables and such.
I’d like one to clip onto a two wire (two pronged, no ground) flat cable like this one: 
Anything like that exist yet?
I don’t know of any off the top of my head, but with a cheap digital caliper and tinkercad, I assume you’d be able to model one fairly trivially. You could friction-fit two halves around the cable, and secure it with some simple adhesive, or some kind of simple bolt/nut fastener mount if you wanted to get clever.
Never not learn a new skill!
I haven’t looked to see if one already exists.
But, like someone else said, this would be relatively easy to model.
I would go about it in a different way; here’s a quick drawing:
Make the loop for the plug side slightly smaller than the diameter of the cable so it’s a super snug fit, and the other side with a large enough gap that you can easily push the cable through it.