It appears the university may have what you are looking for:
The collection does not include recordings for the years 1946-1964,
but they may have information of where or to whom to write regarding
those, if any.
On 8/29/2019 9:07 AM, John Gledhill wrote:
> Is anyone aware of archives or recordings from the New Hampshire Music
> Festival from the 60's / 70's.
> I am preparing the last surviving film of James (Jim) Farnsworth who
> had a business shooting ski movies in the 50's and early 60's.
> Following an accident he diverted his attention to new areas including
> recording the New Hampshire Music Festival.
> I have been in touch with the family, for whom I am preparing the
> film, and with someone currently at the New Hampshire Music Festival.
> If anyone is aware of other archives, the please let me know. I was
> hoping to find some music he recorded to put behind an hours worth of