you need a turntable for the most realistic scratches. You'd then need some software to sample from the turntable, put some vinyl on and scratch, make sure its recording. This is the most authentic way. You could use Serato/traktor etc, but they are not 'real' scratches so to say. Or you could just get loops.
---------- Post added at 03:06 PM ---------- Previous post was at 03:05 PM ----------
oh, and no, traktor/serato can not be used as a vst from what i am aware.