There are many websites which offer you to download 3DS ROMS free. Before downloading 3DS ROMs, keep in mind that:
- If you are using flashcarts like SKY3DS, Gateway 3DS AND Stargate, .3DS file is required.
- If you are using R4 flashcart, .NDS file is required and R4 play DS games.
- If you are using CFW on your console, .CIA file is required and you can play any 3DS ROM or game easily free of cost.
- If you are using computer and want to play 3DS games then use an emulator. I would suggest Citra and downloaded the listed 3DS games that work perfectly on it. Only decrypted 3DS ROMs work on emulators.
Choose 3DS games according to your console and emulator which will work on your system perfectly. There sites will help you to with that: