This a great costume purchase and/or rental store on Roosevelt at about NE 71st St called Vintage Costumers that has all kinds of period clothing - it runs the gamut from old style European gowns and finery to Catholic school girl costumes. I've rented from them in the past. It's on the west side of Roosevelt just north of NE 70th so near the Whole Foods store.
The only drawback is since so many of the costumes are one of a kind you may not find what you want in the size you need.
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