The bad news is there are no mods (that I know of) for Macs.
The good news is you can use any mod with a Mac if you do multiple installs of HoI. Then you can overwrite the vanilla files with the modded ones and play away.
This may seem a bit of a pain, but it's actually handy if you're into mods designed for different versions of the game. It's pretty much the only way to enjoy (say) a DD mod, a HoI2 mod, and an Armageddon mod on the same computer.
Deo Vindice Mod(Play as the CSA in HoI3: Their Finest Hour):
Read about it here. Download it here.