I am going to say it anyways, but Apple.com. You may not receive the discount you’re seeking, but you know you’re purchasing a legitimate product, especially in the market when there are so many different types of fake cases, it’s just a ‘safe bet’ purchasing from them. If a discount matters that much to you, then utilize sources like eBay, but watch for counterfeit Apple products and review sellers history.
I was able to find one at Best Buy a while back but it was the last one they had. Maybe you could throw something up in the Marketplace here. Someone might have a lightly used or new one lying around.