The music for Going Rogue was composed by
Jason Graves, though it's unclear if he composed
all music introduced since then. It seems likely to me since most music (at least for the zone neighborhoods) shares thematic elements. Also unclear is whether the music was composed as "work for hire," which would make it the property of NCsoft, or as "commissions," which would remain the property of the composer.
Generally, though, all music and sound work went through Austin, so that would probably be the first place to ask.