Dear Ms. Poppiti,
Thank you for posting your request on History Hub!
We suggest that you use WorldCat to locate copies of and information about the plays you are researching. Please search for titles like "Bandit King", "The Boy Scout", and "The Outlaw Brothers", and you also may search for playwrights such as James H. Wallick N.S. Wood, Thomas F. Daggett, and William F. Carver. WorldCat has subject headings for Equestrian Drama and for some of the authors that may be helpful, too, and WorldCat Identities offers additional information on individuals such as Wallick, James H. 1839-1908 , Wood, N.S., Thomas F. Daggett Carver, William F. 1840-1927 (William Frank).
In addition, please search historical newspapers online via the Library of Congress’ Chronicling America website. We located 72 references to "Steed of the Delawares" and 19 references to "Boy Scout of the Sierras", for example. You also may be able to access historical newspaper databases or websites at a public or university library.
If you are able to identify particular locations where the plays were performed, we also suggest that you contact local or state historical societies to see if they can offer you additional assistance. History Nebraska, for instance, has some records related to William Frank "Doc" Carver that may contain relevant information.
Finally, Yale University Library offers a number of drama resources online, including this one for Finding Play Scripts, which might be useful, and you may wish to contact the National Cowboy & Western Heritage Museum to see if they can offer you additional assistance.
We hope this information is helpful. Best of luck with your research!