COSTUMES & PROPS
Theater
Harry Ransom Center, University of Texas at Austin
The Costumes & Personal Effects Database includes some costumes. Select "Gordon Conway Papers" or "W.H. Crain Costume and Scenic Design Collection" for theater costumes.
University of Bristol Theatre Collection
The Mander & Mitchen Collection has over 70 costumes, described at the item level. Click on the prior link and select the "plus" button next to "Costumes" in the hierarchy to see inventory. There is also a series of props cataloged under "Objects," but they are not yet described at item-level.
Dance
New York Public Library, Library for the Performing Arts
The NYPL has a few dozen dance costumes and ballet slippers,
ranging from costumes for Isadora Duncan and the Ballets Russes from the early 20th century to the Joffrey Ballet in the
late 20th and early 21st century. These materials are not indexed in a single document, but you can go to the main Research Catalog, search for "costume," and limit format to 3-D object.
Harry Ransom Center, University of Texas at Austin
The Dance Collection (1827-1900 [bulk 1910-1960]) includes costumes; go to the Costumes and Personal Effects Database (linked above) and select "Dance Collection."