Plug your vin into mopar parts and look up nerf bar, step rail, running board, etc as search strings. They are replaceable for a lot of vehicle, IDK about your truck.
If that doesn't get you anywhere, I would look on ebay. Manually plug in your search strings as above, plus try pad, step pad ...anything that you think will provide a resut.
I had a similar thing happen on my Hummer. I was eventually able to find an ebay seller that had one. It was like $45 ...a little steeper than I was hoping, but it was worth it and ..been on the truck now for a few years. No problems.
If you know who the original mfgr was of the part, you could contact them too. Summit and others sell rubber/plastic replacement steps pads. Try a google search too. Maybe you'll get lucky and find a brand new one that matches what you need. Bear in mind there is a bazillion different styles. Does yours have a part number on the under side (and a mfgr name??)?