I watched "The Odd Angry Shot" the other day, based on the recommendations here. An interesting film, but as others have pointed out, nothing like SAS operations in South Vietnam.
I can also recommend "Sleeping With Your Ears Open". Based on the descriptions of patrols in the book, a realistic SAS film would be rather boring and devoid of dialog - at least in the jungle. Back at base might be a different matter.
Several days of patrolling completely silently with using only hand signals and little or no contact with the VC or NVA, other than observation, makes for great reading but a poor film.