Instructions
Start "Pokemon Sapphire" and obtain a Pokemon from Professor Birch. Travel to Rustburo City and defeat Roxanne, the first gym leader. Go to Dewford Town and beat the second gym leader, Brawly. Get the Dynamo Badge from Wattson, the third gym leader, in Mauville Town.
Beat Flannery, the fourth gym leader, with a Water- or Ground-type Pokemon. You will find her in Lavaridge Town. Flannery will give you the Heat Badge. Leave the gym and you will bump into your rival. After exchanging a few words, she will give you the Go-Goggles.
Wear the Go-Goggles to access Route 111, which is north of Mauville City. You couldn't access the desert route before because the sandstorm would harm your eyes. Look for the man on this route who is standing next to a vine tree. He will give you TM43, which is Secret Power.
Fly to Slateport City and head to the Slateport Market. Since you have Secret Power, a new shopkeeper will appear in the middle-right side of the Slateport Market. Buy additional Secret Power Technical Machines from him for 3,000 PokeDollars each.