First off, if you don't find the song your looking for, try typing the just the name of the artist.
Also, try soulseek instead of Kazaa (if thats what you have) www.slsk.com Or winmx, www.winmx.com

Well, it depends, you gotta find what your into, their are many different styles in underground rap. Horrorcore, hardcore, battle emcee, etc. etc.

Download
Cunnilinguist - 616 Rewind (Just type in 616 Rewind)
Smut Peddlers - Tower Of Babble (Their is a rock banned called Smut Peddlers, if you hear some like heavy metal type shit, you got the wrong band lol)
Necro - Poetry In The Streets (Or
Rise - Know (Its hard to find his shit with Kazaa and that, use soulseek, or winmx)
Kool G Rap - The Streets (Not to sure what you have or haven't listened to yet)...