The Korean Mafias are usually named something-PA.
It's usually the geographic region they operate in, followed my pa (which means roughly clan).
I used to live in Taegu, and there was a street there named Joong Ang Ro. So they were the Joong Ang Ro Pa.
Now, as for how they get their money, it's the same everywhere, right? The lower ups kick it up to their superiors. The head honchos have ties with government, conglomerates, etc. The mid range guys own clubs, bars, conduct illegal gambling and prostitution. And the lower level thugs make sure all debts are collected, while occasionally beating the *&^% out of the occasional student to take their money. We used to call these lower level thugs Ggangpaes. Not very widespread though, if you are smart enough to avoid certain areas, then you'll be ok. If you are a dumb @#!* enough to wonder into ggangpae territory, then you should have your money taken