It would be a legal no no for us to tell you how to find back up files of Dreamcast games, so we won't be doing that. Hey just thinking out loud: You know something I like to do in my spare time? Peruse Archive.org. How about you?
Games we recommend include: Sonic Adventure and its sequel, Skies of Arcadia, Jet Grid Radio, Marvel vs. Capcom 2, Resident Evil — Code: Veronica, Power Stone 2, Soulcalibur, Crazy Taxi, Rez, Shenmue I and II, Samba de Amigo, Space Channel 5, Seaman, Grandia II, Sega Rally 2, and Tony Hawk's Pro Skater 2.