I should add to this thread that when I was doing research for the TV/Film articles on the BBs that I contributed to ESQ-I got in touch with the David Frost archives and the Carson archives people. They were quite nice and took the time to answer all my questions. As I feared-the "Lost" Frost app from May 1971 where Dennis performed "Forever" and "Lady" and the BBs sang "Vegetables" was indeed destroyed. Clearly-however-there is an audio tape of this app-since it has been booted. It also had a cool interview where Dennis discussed filming Two Lane Blacktop. The Carson people also told me the same thing-the BBs made two 1968 apps on the show-with Johnny as host and both are gone. The May 2 68 app would have been fascinating-because it was basically the BBs promoting their about to begin tour with Maharishi and talking about why TM is so great-plus singing "Their Hearts Were Full of Spring" and some "Friends" songs. There is an audio tape of this too I should add-but tragically only the songs not the interview. That being said-it is always possible that a fan made a kinescope of one of these shows that may turn up
The precedent is there for similar items showing up in a fan's collection: The "lost" Monkees appearance on Carson's show has been circulating for decades now on a poor-quality audio, but at least it still exists in some format. The infamous Lennon-McCartney appearance on Carson's program the night Carson was on vacation for the week exists the same way, but as both fan-recorded audio and home movie, which was basically the fan or his/her parents setting up a home movie camera in front of the family TV set and shooting a primitive kinescope at home.
The only thing that diminishes the hope for such a Beach Boys find is that the Monkees and Beatles had a larger teen and pre-teen fan base at the time of those appearances, who would possibly convince their parents to set up the camera and capture their heroes on a late night TV show (especially those past their bedtimes!). I have doubts that a Beach Boys fan who would be interested in TM and meditation would have set up the ol' 8mm home movie camera to capture that as the kids had wanted to see the Monkees and Beatles. I hope I'm wrong!