The 64playersaddon.zip file you have requested: Modifications / Multiplayer / 64 Players Add-On - 372.43kb is not available. Perhaps try browsing all files for the game F.E.A.R. and upload any files you want to share or are missing. This is the only information we could locate:
For more information on FEAR, visit Fear.filefront.com This mod allows you to play on retail servers with as many as 64 players. You can only change the Player limit in your serveroptions file manually, not in-game.