The bands aren’t something you can buy - every day you have to go to a dedicated site with your room key. They then check you against the hotel records and issue however many bands are needed for registered guests. They actually put them on you there and then - you can’t easily remove them, most times you need a knife or pair of scissors. No bands means no access to the pools, slides, chairs, lazy river etc. The CMs are trained to look for the bands.