You can get most of them in Samsung retail stores. Search for an offline store near you, you find most of the official cases.
S21 Ultra s pen case is not even displaying as an item on Samsung shop but its available on Samsung store. Due to covid, Samsung might took that decision of supporting their stores in some way may be.
I have a gift voucher which i can only use online. All other phone cases are available just the s21 cases are not available. So i dont think samsung took any decision due to covid .
