A:AnswerYes you can buy an unlocked iPhone 11 Max however you cannot buy it from Best Buy. Best Buy does not sell unlocked iPhones, you would have to buy it from Apple directly.
A:AnswerOnly way for you to know is to go in store on release day. People will be picking up their pre orders as well as going in to see if they can buy on the spot so go early and hope for the best. Otherwise you may be able to call at opening time on release day to see if they have any extras available. No guarantee that the store will provide you that info though.