Same game Pokemon Blue, I'm on Viridian City go for the 8th badge.
Do you have Pokemon Red & Blue? The cheat won't work on later games like Pokemon Yellow. Here's how to do meet up the MissingNo glitch:
First thing is you have to move the item (it has to be a Nugget, Rare Candy, Master Ball, any potions and revives and TMs to be duplicated, HMs, Bicycle and Pokeflute won't work) into the 6th item by pressing select and move them up to as a 6th item, then if you have a Pokemon that learned "Fly" (HM02), then fly to Viridian City, meet the old guy who teaches you how to catch a Pokemon, when he asks "Are you in a hurry?", answer "NO", then when he shows you after that, then fly to Fuschia City, head down to the beach and use a Pokemon that learns "Surf" (HM03), the swim to the edge and swim all the way to Seafoam Island, don't worry if you face Tentacool on the way, just run, once you made it to Seafoam Island, swim up and down on the shore, wait until the blackness extends for a few seconds, that's when you meet a MissingNo glitch, don't catch it, just run. Then check the 6th item and you'll see it's dupliacted, you can do it again after that with the items only allowed to be duplicated like Master Ball, Rare Candy and Nugget.
I told my brother about the same cheat playing my Pokemon Red game, he tried it out and succeeded.
The cheat is found here on this link:
http://ca.ign.com/cheats/games/pokemon-red-version-gb-9846