Go to you default location for Battlefield 2, look for the FH2 mod folder, there in should be an AI folder, ie:
C:\Program Files (x86)\EA GAMES\Battlefield 2\mods\fh2\ai
In that folder is a file called, aidefault.ai, make a backup before editing this file.
In the file you should have the following lines:
aiSettings.setNSides 2
aiSettings.setAutoSpawnBots 1
aiSettings.overrideMenuSettings 1
aiSettings.setMaxNBots 80
aiSettings.maxBotsIncludeHumans 0
aiSettings.setBotSkill 0.5
Save it and now you can play with 80 bots, hope your PC can handle it