Where can I find robe and shoes (parts of Sorcerer's Apprentice costume)?

This question should be clicked as "Answer Accepted".
SilverX1984 was exactly right.

I got my hands on the Prima Official Game Guide.
The Costumes Appendix is on page 307 (if you want to take a quick peek at a store.)
1) "Sorcerer's Apprentice Hat -- Yen Sid's Lab" (which is the table in the tutorial, before the brooms start moving. "(360 / PS3 only) Earned from Spin Attack tutorial."

2) "Sorcerer's Apprentice Robe -- Disney Gulch (360/PS3 only) Found in red chest at Angel Entrance" (That means if you enter the Gulch on a ledge through a projector screen, instead of through a manhole.) The thinned-out chest is on that ledge, near the lift.

3) "Sorcerer's Apprentice Shoes -- Mean Street South (360 / PS3 only) Available from Mad Hatter after Mad Doctor's Lab boss fight" That is the first boss fight. The Mad Hatter is also called a haberdasher.