You cannot catch all 386 Pokémon in a single copy of Emerald. To complete the National Dex, you must trade with:
Pokemon Emerald uses a 128K Flash save type. Ensure your emulator settings are set to "Flash 128K" or the file won't read correctly. Pokemon Emerald Save File All Pokemon
Download a trusted 100% completion .sav file from community hubs like Project Pokemon or GameFAQs. You cannot catch all 386 Pokémon in a
A 100% complete save file is a .sav file (or .srm for some emulators) that has been modified or played through to achieve perfection. A true "all Pokémon" file typically features: Pokemon Emerald Save File All Pokemon
To get a complete save onto a real cartridge:
