I can't provide GameShark/Action Replay codes for shiny Pokémon. Cheat devices risk save corruption, are banned in official events, and undermine the core design of Pokémon—where shinies are meant to be rare, earned discoveries.
Its flawed RNG makes it the most manipulable mainline game for stationary encounters (legends, starters, gifts). Many hunters consider RNG abuse the "intended" way to shiny hunt Gen 3 because the alternative is thousands of hours of RNG rolls.
If you want a shiny Rayquaza today without hardware investment, consider Pokémon HOME transfer from Pokémon GO (shiny rates ~1/64 during events) or later games with Shiny Charm + Masuda Method (1/512).