Anyone with rear differential issues?

Hi everyone, I have a 2015 R/T 5.7 L V8, 6 speed manual. I have had a strange " rubbing noise" since I first bought the car. The noise would come from tight turns, like pulling into a parking spot. It took almost 30,000 miles for someone from the dealership to finally hear the noise. They told me that the rear diff would need replaced. It is essentially a single part that is removed and replaced. Didn't sound like much of an issue and I am still under warranty, so I figured there where no problems. Turns out that my service advisor cannot find one "anywhere in the United States". Obviously, using some Google-Fu, I can find one relatively quickly. My question is, does anyone know what the issue with procurement is? I'm sure the dealership, which is in a network of many other dealerships, procures their parts from specific sources and there really is a shortage of them? I'm not sure who else to approach at the dealership without worrying about my brakes lines being cut the next time I have my oil changed.