We can't provide you with the ROM of any licensed game, but all valid emulators listed in the rules can be easily found on the internet. Most popular ones are: BizHawk, FCEUX and Nestopia.
Linking to ROM websites is illegal and is against speedrun.com's rules since Super Mario Bros. is still protected by copyright law. Therefore, we can't tell you where you can get the ROM.
However, we can tell you where to get the emulator. The leaderboards allow runs done on BizHawk, FCEUX, Nestopia, and OpenEMU. You can get BizHawk, FCEUX, and Nestopia from the Resources page. https://www.speedrun.com/smb1/resources
For ROM just search it up in your search engine. You can tell if it's PAL/NTSC because in PAL the music goes fast. I hope I'm not breaking any rules by saying that
Effective immediately, any submissions using the SNES9x emulator will not be verified. The SMB1 mod team has concerns about its integrity due to its ability to overclock and remove lag frames, which may not be easily detectable. Additionally, we request that all BizHawk submissions avoid using the S
