To be honest, Congo Natty never really made what most people consider "ragga." X-Project came the closest of the CN offshoots, but even then it wasn't much.
One important thing to consider is what does your friend consider ragga? Is he more into the earlier styles, like around '93, or when ragga was becoming quite predictable, around '95? Also, is he just interested in ragga, or is he also into oldskool and hardcore?
Names for your mate to look into:
King of the Jungle (Dextrous & Rude Boy Keith)
Amazon II / Aladdin
Kemet (the label)
Cutty Ranks, Barrington Levy, Beenie Man, Elephant Man, Top Cat, Supercat, etc. are all dancehall vocalists that have done nuff ragga tracks. Takes a bit of digging to separate the dancehall from the ragga though.
Anyway, some of those producers will have done mostly oldskool jungle, but most of em are ragga heads. Lemme know what he thinks :thumbsup: