According to the Dictionary of Marketing Terms of the American Marketing Association, a catalog showroom is "a retail outlet that consumers visit to make actual purchases of articles described in catalogs mailed to their homes or available for reference in the store".
There is usually a wide range of goods on display, reflecting the range of goods offered in the catalog. The sale of the items is conducted in the store, so, as separate establishments they should be classified as stores carrying a variety of goods, i.e. in 5219. If the range of goods is limited, this establishment could also be classified in the corresponding class of group 523.