ECCO has digitalitized images of works published in the UK during the 18th century and from elsewhere (books, pamphlets, essays, broadsides, etc.); this collection is based on the ESTC (English Short Title Catalogue). A keyword search for "prompt books" will return results which include prompt-books for shakespeare. You can search within the results for shakespeare prompt-books.
Macbeth Onstage contains an introduction, a list of publications which had reviews of the production, cast list, an account of the performance, facsimile of the promptbook, and interviews with actors. Numerous illustrations of the production are included as well.
The Prompt-Books contain an introduction, collations, and partial text of reproductions in collotype facsimile for King Lear, Henry VIII, The Merry Wives of Windsor, Twelfth Night, The Comedy of Errors, and The Winter's Tale.
All eight volumes of Shakespearean Prompt-Books of the Seventeenth Century are available online. The prompt-books are presented as facsimiles. The online version contains the introduction, collations, and acts as found in the print version. It is possible to perform a search within the prompt-books. Mullen Library also has Volumes 3, 5, 6, and 8 in Stacks Folios (PR2757 .E8).