Drama Online's Advanced Play Search allows you to search for monologues of a given gender and word count within 2,672 scripts of classic and contemporary plays. It turns up at least 2,166 monologues.
Our subscribed collections include, for playtexts (scripts), the Core Collection (works published by Bloomsbury, Methuen, Arden Shakespeare, or Faber and Faber), Aurora Metro Books, Nick Hern Books Modern Plays, and Playwrights Canada Press.
We currently have the following monologue collections through the EBSCO eBook platform:
We have hundreds of ebook versions of scripts and script collections through our subscription to the EBSCO eBook Collection.
None of these are published, unfortunately, by Samuel French or Dramatists, but many are published by Theatre Communications Group, among others.
While no simple search can bring up all scripts and only scripts, the first, rather complex, search linked above gathers a pretty good set of the scripts we have on that platform, while the second link above has just those published by TCG.
If you view the ebook in EBSCO's embedded viewer, you can use options at the very top of the screen to download PDFs of selected pages. (The option exists to download the whole ebook but requires creation of an EBSCO account and, often, installation of additional software and could make the book less available to others for two weeks.)