I can't find a single place to buy one. :/
I got lucky at Target. None of the other stores near me seemed to know when they would get more. Target seemed to have the best handle on new shipments coming. I walked into the store around 9:30am and they had their new stock sitting on the counter behind the register (2 black and 3 red).
I was surprised how clueless my local Best Buy was about their shipments, they used to be my go to for things like that. Their display case was still full of the regular 3ds XL and 2ds.