costumer

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One that makes or supplies costumes, as for plays or masquerades.
• noun A clothes tree.

from The Century Dictionary.

• noun One who prepares or arranges costumes, as for theaters, fancy balls, etc.; one who deals in costumes.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who makes or deals in costumes, as for theaters, fancy balls, etc.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A person who designs, makes or supplies theatrical costumes; a costumier

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun someone who designs or supplies costumes (as for a play or masquerade)