Some folks are posting pictures of "Flares" so I put this here anyway. If inner rear wheel well liners are what you're looking for this is it.
When I purchased my 2019 Ram 2500 6.7L Bighorn I headed over to parts at my dealership and had them look up rear liners, called "splash" when you ask. Of course the dealer said they weren't available for my model since he searched under 2019 for the parts. Me knowing this already I asked him to look under previous years. He then was able to locate the part numbers and was able to order the splashes for me. I still haven't put them on yet since I'm not sure if a buyback of my truck, another story, is going to happen. Anyway, here's pictures showing what I purchased and the part numbers. I did do a search through online Mopar, not all, and this is what I ended up finding, not available. https://www.moparpartsgiant.com/parts/mopar-splash~68453299aa.html
, however with this information it should help anyone looking with a place to start. If you are lucky to find some keep in mind that a dealer charges $7+ for each for the 12 screws needed to install them but NAPA part stores have them in stock for much less.