you must have rotom first in your party then talk to the elevator
Safron city
go to the silph co
in saffron city
beat red and go to silph co.
still in silph co by the door he will want to trade a forrtress for a beldom
Silph Co.
In the silph co.
Receive from Steven Stone in Silph Co. HOPE IT HELPED !!
After talking to him there he'll be back in Silph Co. near the entrance. :~)
You can't battle him. But if you go to Silph Co. after defeating Red, you might see him there.
i'm not sure in soulsilver but in heartgold after seeing him in the pewter museum you can trade him at silph co
Silph Co.