Where to buy replacement housing

The problem with a branded housing is that it has an apple logo on it, which is copyrighted, making it illegal to manufacture. You can either buy a new unbranded housing, or a branded used but high quality housing. iFixit sells unbranded ones here iPhone 7 Blank Rear Case. (I just put that there to help others who come to this page later on). You mentioned that you needed a branded housing, and that probably won’t be of much use to you. For branded housings, I have always found good branded housings on eBay. I would try searching there