Well if he does not mind hunting behind hi fence I would recommend Spiral Horn Safaris in the Limpopo area of South Africa.

If he wants free range kudu, then Namibia would be my pick hands down. As mentioned by Nitro X, Karl Stumpfe is well known and I would also ad Dirk Rohrmann. I hunted Namibia and it was exceptional. Would go back there in a heart beat.