There are a number of companies like Reelin' in the Years which collect and license video footage for commercial use. They don't sell to private collectors but they market the material for specials and home video releases and for use on other shows and such. They've been offering the archives of The Merv Griffin Show and now they're handling The David Frost Show.
Frost hosted this series on American TV from 1969 to 1972 — and it got a certain amount of publicity due to the fact that he simultaneously lived in and did another show in Great Britain. He would literally make a transatlantic commute each week to the U.S., tape several shows, then fly home. I believe in the middle of doing all that, he even went to Hollywood for a few days and did an episode of Here's Lucy wherein Lucille Ball's character was hired to accompany him on those flights and guard him from intrusions so he could sleep.
Frost's U.S. talk show came about because Merv Griffin, who was a hit with one in syndication, accepted a deal from CBS to do a late night network show opposite Johnny Carson. Group W, which had syndicated Griffin's show, hurriedly threw together a show with Frost to offer to stations which now had that hole to fill in their schedules. The Frost show was 90 minutes but was also offered in a 60 minute version that ran in some markets.
The emphasis on the Frost show was less on comedy than on hard-hitting interviews and his producers did manage some incredible guest bookings, as you'll see in this sizzle reel. I hope some cable channel starts airing these programs in their entirety…