I found this 1978 interview online:
https://www.worldcat.org/title/oral-history-interview-with-harlan-howard-1978-december/oclc/58841227
I found this 1978 interview online:
https://www.worldcat.org/title/oral-history-interview-with-harlan-howard-1978-december/oclc/58841227
Do you know of any others?