Step#1: Go to Viridian city and talk to the old man and he will ask if you want to show how to catch a pokemon, Say no.
Step#2: Fly to Cinnabar Island and surf on the RIGHT COAST!
Step#3: repeatedly Go Up & down on the coast, sooner or later you will encounter a pokemon called Missingo, or a pokemon over lvl 100, DO NOT CATCH IT!!!
Step#4: Run away
Step#5: Now in Your invintory, the 6th item in it will have a weird symbol. Congrats!
now you have 999 (give or take 500, lol) of that item (to change the item press select and
go to the item you want to switch)