Try this, you stupid people. lol
Make sure you haven't beat the Gambler outside of Lavendar Pass or the youngster above Cerulean with the slowpoke.
Go into Lavendar Pass, and come out. SAVE AS SOON AS YOU COME OUT THE DOOR. Walk gently up to the gambler. As soon as he sees you, hit start and fly to Cerulean. Go up to the youngster and make him battle you. DON'T GO IN FRONT OF HIM! MAKE HIM WALK TO YOU!
Win against him. Fly to Lavendar. Procedd west to where the gambler is. Your menu should pop up. Close it. You should get attacked by a level 7 Mew. Catch it. Rejoice.