A way of getting slavery involved could be using immigrants and foreigners as slaves, seeing that this is a radical nationalist group. Those who support it certainly won't hold their support back because the outsiders they hate are not kept out, but are forced to do labour for them instead.
You're right though, maintaining secrecy first off could be a good idea, dependant on how radical actions this group would commit.
And yeah, the Confederacy in Starcraft was something I deem an epic concept too, but I personally prefer faction/player group ideas taken from other games kept to a minimum. Just base it on the CAS, which is an RL element, most adequate for the Freelancer universe.
