The Extraordinary Bolt can be found behind a Black Stone Wall near the place where Olimar found the Yellow Onion, nine Bomb Rocks are required to destroy the wall.
"It's the Extraordinary Bolt! I bought this incredible bolt because the salesman told me it is of extraordinary quality that is indiscernible to the average person. Exactly what makes it so extraordinary is a secret. But just look at it! Extraordinary!"
"This bolt's bolt holds the kind of value that only a true connoisseur can understand."