Put the item 6th in your list. Fly to Veridian City and talk to the old man and let him show you how to catch a weedle. Afterwards, fly to Cinnabar Island and surf up and down the East side. Eventually a Pokemon at a level over 100, or a Missingno, which looks like a microchip, will attack you. You can catch the normal Pokemon, but not the Missingno, as it will ruin your game. If you don't want to catch them, just kill them. Your bag will then say you have 99 of the 6th item, but you have 9 99s of the item.