If you import your new data into a different table, You can define a relationship that matches records by Manufacturer and Style number between the two tables. Then, records in your original table that do not have a matching record in this temporary import table would be records for items that have been discontinued. You can perform a find for such records and then delete them or you can set a field in each such record to a value that marks them as discontinued.
If you have a field that auto-enters the modification date in your table, you might be able to do an Import Matching records import with auto-enter options enabled. After the import, any records with a modification date earlier than the date of the import records did have a matching record in your imported data and thus should represent your discontinued items.