all u need to do is get all 16 badges and prof. oak will call you and tell you to go to his lab. u will get rock climb and he will also unlock mt silver. NOTE: u dont need rock climb to get to blaine...
You get it from Professor Oak after you beat Blue ( the Viridian Gym Leader.)getting your 16th badge. Go to Pallet town and talk to him. after that you can go to Mt. Silver.