[Dan Hibiki]

Kaiobito doesn't know where the Hell New Namek is, either. The new Guru of Namek doesn't have the level of power the old Saichourou has, either, because he was the father to the entire race, and had deep psychic connections to only what is happening on the planet he is on. Even if the new Guru of New Namek had Saichourou's powers, it still wouldn't suffice. Dende would not be able to contact New Namek.

You must also consider the amount of time it would take. What if a message COULD be gotten through to the Guru on Namek? He would have to contact the six elders, and then the Dragonballs would have to be assembled. It takes a few days at the very least to fly from some of the villages to others, so it would take over a day AT LEAST to assemble the balls. By that time the battle would have concluded. You see, by the time the DBZ fighters would come to realize that they would need the Dragonballs, Gill's organization would have already ruined the Earth set, and the battle would be to the point where the DBZ fighters would not hold out much longer.