Taking a brief foray into the Transcription Service of Armed Forces Radio this week. Here is a recording of a concert at the Hollywood Bowl by The Los Angeles Philharmonic, guest conducted by Walter Hendl and featuring legendary violinist Issac Stern in a performance of the then-newly discovered Violin Concerto Number 1 by Bela Bartok.
The concert was recorded during the 1961 Hollywood Bowl season. Stern recorded this piece for Columbia Records with the Philadelphia Orchestra, conducted by Eugene Ormandy also in 1961. I doubt this particular performance has seen the light of day, so it's something of a rarity for Stern collectors.
And even if you're not, it's still rare and the recording probably hasn't been heard in some fifty years.