Search for "Universal Pokémon Game Randomizer" on GitHub. It is the industry standard tool for Generation 1 through Generation 5 games (including SoulSilver). It is a safe .jar file that runs on Windows, Mac, or Linux (requires Java).
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Most reputable modding communities do not distribute pre-randomized files. Why? Because the randomizer is customizable. One player might want a run where every Pokémon is Legendary, while another wants a balanced "Nuzlocke" run. pokemon soulsilver randomizer rom download