Add a custom field to Inventory Items. Label it Supplier. Set it to show as a column. Now your listing can be sorted by that column, either before or after exporting.
Or search for the supplier’s name. You will get a list of only those entries with that name. Just be sure the name is unique. Otherwise, items from Acme Paper Supply Corporation and Acme Food Products Company will both come up.
You can always export and manipulate, sort, delete, or whatever in a spreadsheet.