Kill a lot more than 30 Xenos...and the odd bribe helps as well (but that is a bit hard at the early stages...who can afford a 100,000 cred bribe when you are struggleing to break 20,000 creds!!!)

We don't really own this place, just break a few arms if we have to - Bounty Hunter Mitch Murphy, Bonn Station.

Junkers are hard to 'join', there are always a few posts with people looking to join them. Like Merchant said the only thing to do is kill more xeno's or, for a bit of variety, go to kusari and take out some hogosha. However why not go for another bad guy posse? There are plenty of groups who are easier to join than the junkers at the start.

I think the problem with the junkers is that their only two enemies i.e. hogosha and xeno's are enemies themselves. Therefore when you kill a xeno your rep goes up with the junkers and hogosha. Say your rep improves 5% with junkers and hogosha, because hogosha are enemies of the junkers this decreases your rep with the junkers - say by 2%. Net result improvement by 3% with junkers. I am possibly wrong about this i'm not certain there is a knock on effect.