I have found some histories for SOE and certain individuals inside SIS, but not much. Can anyone recommend any articles or sources about SIS and SOE in WWII? For SIS, any intelligence gathering or other operations they may have run against the Axis (Germany, Italy, or Japan). For SOE, about their formation, planning, and how they looked for recruits.
Keith Jeffery's MI6 is the authorised history of the Secret Intelligence Service from its founding (as the Secret Service Bureau) in 1909, up to 1949 and the early years of the Cold War. There's a lot of material on the war years in there, and it's a thoroughly good read overall.
On the SOE, check out the work of M.R.D. Foot, the Executive's official historian. SOE: The Special Operations Executive 1940-1946, but he also wrote separate volumes on their operations in France and the Low Countries.