While no longer sold individually, you can still obtain the original "USA (En, Fr, Es)" version legally through specific bundles or platforms:
: You can purchase the original game as part of the Sonic the Hedgehog Legacy Bundle. If you already owned the "Sonic Generations Collection" before delisting, it remains in your library for redownload. Xbox (Series X|S & One) Download Sonic Generations (USA) (En,Fr,Es) | 3...
If you are looking for the most accessible way to play on current hardware, is the current standard. Sonic Generations Collection on Steam While no longer sold individually, you can still
: You may still find digital download options or physical copies for the 3DS version on the Nintendo Store or through third-party retailers. Modern Alternative: Sonic X Shadow Generations While no longer sold individually