You won't find FIFA 99 on modern digital storefronts like Steam or the EA App . Licensing issues with player names and music usually prevent these old titles from being legally re-sold.
Communities like MyAbandonware or the Internet Archive often host the files for historical preservation. These sites are the "go-to" for those trying to find the full PC version for free.
For many PC players, it was the first time they could easily mod players and teams, sparking a massive community of creators. The Search for the "Free Download"