I love SWAT, but sometimes would like to be able to trade some tactics for action, i.e. play the "barricaded suspects" game mode from multiplayer, but with bots. Does anyone know of AI bots for SWAT 4 multiplayer or perhaps a mod for the game that would add a single-player deathmatch-type game mode, like barricaded suspects?

Chances are slim, but maybe there is something like this. ;)

As of now unfortunately there is no such mod.

Have you tried making a custom game, you can create them from the main menu and set up all the rules for one there. (Map, Victory Conditions, Enemies, Hostages, Friendly Team and so on)