I think you're talking about A Smattering of Intelligence (Season 2- and if you have the DVDs, it's on disc 3). I believe that's the one where Colonel Flagg and another government spy are put in the same M*A*S*H and they both think that Frank is up to something. I remember it's the one where Colonel Flagg breaks his arm to stay at the 4077th because they told him that he had to leave if he didn't have any injuries, hahaha.