Buy the standalone Sonic 3 & Knuckles on Steam.
If you previously purchased Sonic 3 & Knuckles on Steam before the 2022 delisting, the Sonic 3 A.I.R. installer will automatically detect the official ROM file in your Steam directory. Alternatively, you can use a retro cart dumper (like a Retrode) to legally rip the ROM from an original 1994 Sega Genesis cartridge you physically own. sonic 3 and knuckles steam rom download best free