I designed this piece and have .STL files I can send to anyone interested, just pm me. I had the driver's side fall down in November, found this thread and saw that nobody had a solution available. Went ahead and designed it, had a friend print it and successfully been working in place since. Then just in January, luck of the draw my passenger side failed in the same manner.
With that said, I have both top/bottom/left/right designed that should fix just about any of the rear quad cab window clips that could fail.
If you feel inclined to pay for my efforts, just donate whatever you want to a good dog rescue in your area