The second program of the original 1970-1995 series – aired July 11, 1970 – is thought to be lost, although later, a "July 11, 1970" program was supposedly created featuring segments from shows aired in July and early August, 1970.
The master recordings to Casey's Top 40, the countdown program hosted by Casey Kasem from January 1989 to March 1998 (following his August 1988 departure from AT40), are completely gone, according to the show's production company/rights holder Westwood One Radio Networks. Though the entire series circulates via vinyl/CD copies distributed to radio stations (and, as such, can be found on YouTube), the episodes themselves have not been broadcast over any actual radio stations since their initial airing.
Although all programs from the Shadoe Stevens-era (1988-1995) exist, they are not owned by Premiere Radio Networks, owners of the American Top 40 franchise since 1998 (when they were known as AM/FM Radio Networks); instead, they are owned by Cumulus Media (successors to the show's original production company, ABC Watermark; interestingly, Cumulus now also owns Westwood One, owners of Casey's Top 40). A video uploaded by D'Shadoe to his personal YouTube account in 2015 seems to suggest that his episodes may soon be syndicated to various radio stations as a rerun package, in the style of Casey Kasem's American Top 40: The '70s/'80s. In the meantime, like the above, episodes can be found on YouTube.
All episodes from AT40's sister program, American Country Countdown, are believed to exist in its entirety from the show's beginning (since 1973), but – aside from the trading circuit or various download services – they have almost never been replayed. Those that have probably are the occasional specials – as opposed to regular weekly programs – and usually on small, rural stations. They finally began airing as part of "ACC Rewind", a feature which airs a random show from any point between 1990 and the early 2000s alongside an episode of host Bob Kingsley's successor show, Bob Kingsley's Country Top 40.
Tales by the Fireside, a popular BBC world service radio programme of the narrator's (Lionel Marson M.C.) experiences as a soldier during both World War II and the Great War. Despite being effectively the voice of the BBC's world service, and thus Britain, during his time with the station, no copies of the programme are known to have survived to this day. Even the name of Lionel Marson is less than well known, due to his being active on air at a time when mentioning one's name while broadcasting was considered extremely poor form. At the time, he was simply recognised by his voice. This tradition was first broken only shortly before he retired.
The current generations of his family are actively searching for recordings.
Many of The Firesign Theatre's live radio performances, such as their Hour Hour shows, contained music that was legal to broadcast live but means they can't be sold as aired. The official Firesign archivist is editing much of this material for just that reason.
Radio Mystery Theater.
Paul Harvey's News and Comment and The Rest of the Story shows. His website used to have some archives, but the site was taken down after he died. Paulharveyarchives.com used to have several shows, but the site has been "in transition" for several years now.
Since 1986, The Bob & Tom Show has released albums that compile popular recent skits, guest appearances, songs, etc. at the rate of at least one per year, as well as Greatest Hits Album-style compilations for particularly popular characters or topics. All of them go out of print within a few years and their Unintentional Period Piece nature renders reissues out of the question (even more so for the collections made before the show went national in 1995, because they included many Indiana-specific skits/songs), so completist fans must go to Ebay to track the older ones down. Worse, two early titles (A Day at the Race! and Good Morning Saudi Arabia) were cassette-only releases.
Vivian Stanshall (late of The Bonzo Dog Doo Dah Band), made numerous BBC radio sessions for the John Peel Show, featuring comic monologues and songs, mostly based on his "Rawlinson End" concept. There have since been an album, a book and a film of Rawlinson End, but although the BBC has released lots of other "Peel Sessions" on CD, Stanshall's remain in the vaults apart from the odd rare broadcast and bootlegs.
The radio version of Another Time, Another Place only seems to be available through the academic database Box of Broadcasts, which can only be accessed via British universities.
Many compilation CDs of I'm Sorry I Haven't a Clue are available, but they don't feature the complete episodes. In particular, the earlier ones never contain Pick Up Song, which requires the team to sing along to a recording, due to the reproduction rights. Apparently, in 2010 something changed, and compilations from Volume 12 on do include it.
All of George Orwells broadcasts from the BBC during the war are lost. Most of them were not seen as worth keeping and because of his wartime wound to the throat, he did not sound entirely radio friendly.
The Tomorrow People had a series of audio dramas featuring the original 1970s cast, produced by Big Finish productions (well known for their Doctor Who audios and other fandom series). Five series of audios were released on CD, and during production of the 6th series, their license was revoked. They had to remove all sales links from their site.