You can download a PDF file of it. AbeBooks.com was my source but shipping from Britain is pricey now. Reprints are available from Amazon if you want an actual book in you hands. The gist of it is only 36 pages in length.Swarming and its Control and Prevention by L.E. Snelgrove is a book that I'm currently intrigued by.
You can search up a fair bit of discussion of it here on Beesource. I have been in on a few of them. It works well.