I ordered the
ALTBET Box Handle and Grommet Kit Fit for Dodge RAM 1500 2500 3500 Replace 68054996AA 68054997AB from Amazon for $45. This contains the 2 each of the 68054996AA and 68054997AB (4 pieces total) that are needed. Installation time was 10 minutes total. You can get genuine Mopar parts from your dealer, but they were around 2X as much -- as these parts are so simple I was fine with after-market. NOTE: My truck has RAM Boxes; I haven't checked to see if this works on non-RAM Box trucks.
These parts say they aren't to be used on the DT trucks that we have. I have heard that this is because the divider can obscure the tail lights from some angle when used as a bed extender. Or maybe the tail lights are obscured somehow when the tail gate is down? I didn't notice any issue on my truck. Maybe others can comment if they have seen a problem. In any case, using the bed extender seemed much safer than leaving the tail gate down and only relying on tying down my cargo.
Here is a nice posting showing how the parts are used:
https://5thgenrams.com/community/threads/multi-function-tailgate-bed-extender-not.21570/post-311652