Thanks to everyone for responding.
Amorette Allison’s recollection led to the webpage https://mhs.mt.gov/research/collections/archives stating that the Montana Historical Society has so far collected more than 2,300 oral histories and is looking for more, to the extent that they are willing to loan recording equipment. This appears to be the best and maybe only real repository for oral histories in Montana.
Regarding the interviews of Albert Bender and Wes Munsell, the hosting internet site www.milescityvoice.com apparently no longer exists. If their videos are again located, transfer to the Montana Historical Society obviously should be considered.