Oh, I got something useful pokemonfan! The reason I'm buried in star pieces, is because the dowsing machine is always my main app. Here's a few locations for ya:
Now, go to Iron Island and collect Star Pieces. Heres the list (Hidden items, restock themselfs daily!):
Find Star Piece southeast of the house, in the small rock.
Find Star Piece on the first floor down (to the right from the entrance), near
the center, to the right of a rock and two barrels.
Find Star Piece on the second floor down (the smaller area to the right from
the elevator), near the southeast corner, a few steps to the right of the
barrel.
Find Star Piece on the second floor down (the larger area to the left from the
first elevator), toward the southwest corner, on raised ground, south of Worker
Quentin.
Find Star Piece on the second floor down (the larger area to the left from the
first elevator), toward the southeast corner, in the right of two rocks.
Then go to the ironworks and trade the Star Pieces with the man for one of each shard! Simple!