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
Following investigations regarding the accuracy and integrity of FCEUX, the SMB1/2J moderation team has decided that FCEUX will not be permitted for future submissions, effective September 17th, 2023. The accuracy of FCEUX has come into question following 108Pi's discovery that the current SMB1 Warp
