Instructions
Get to at least level nine and no higher than level 14.
Go to Six Island. This is also known as Fortune Island.
Head north on the Water Path. You'll soon reach the Green Path. Go down this path and you'll reach the Pattern Bush.
Search around the Pattern Bush. You'll encounter Spinarak after a while. This Pokemon only appears about five percent of the time. Keep hanging out there and be patient.
Fight the Pokemon to wear it down. Capture it with your poke ball.