Rock Auto, Ebay, various other online retailers have it. Any Napa, Advance Auto, Autozone, or Oreillys will also have it, and can be ordered from them online. Most places sell it in a kit with the pan gasket, flat filter, and spin on filter. Is your truck a 4wd or 2wd? There is a difference in the flat filters. The 4wd version has a longer pickup to accomodate the deeper 4wd pan. The 2wd version will not work on a 4wd and vice versa.
OEM on Ebay
Various others on Ebay
I never really used the OEM version (except for the change I did a few days ago because the mood struck me and the Dodge house is a block from my house), because Im not a fan of the RTV gasket and all the other kits have gaskets. Im also going to cuss myself in 50,000 miles when its time to scrape that RTV off but, oh well its worth it to be lazy for a day lmao. Even though I always used non OEM Ive never had the drainback problem, if Im not mistaken this was only on certain dealer and wix filters and should have long since been fixed.