Take a look at the link below, scroll down to 'Original Boxster Wind Deflector' - I believe we carry the individual ones. If you like, please feel free to give us a call at 888-280-7799 and one of our Porsche part specialists will be happy to assist you and confirm that the part will work on your '98.
https://www.pelicanparts.com/cgi-bin/ksearch/pel_search_2016.cgi?command=show_part_page&make=POR&model=1042§ion=bdycon&page=1&bookmark=1&part_number=000-044-800-78-OEM