There are not that many spy short stories in the catalogue. All I have been able to find are the real life stories of Taft and the short stories William Le Queux and E. Phillips Oppenheim. Ashenden stories (Maugham) are yet a few years from going into public domain. However, Fred M. White (the guy who wrote those wonderful disaster stories from London) has published a few spy stories.
They are not available from gutenberg yet, but feedbooks swears that they are PD in both Europe and the US
http://www.feedbooks.com/book/6700/the-romance-of-the-secret-service-fund
Also, if somebody knows of a PD writer of spy stories I would be interested in hearing from them. I am primarily interested in short stories.