Glad you are interested in this!
Flanders and her colleague Marguerite Olney also traveled throughout Maine, NH and upstate NY. She collected over 3000 recordings.Many singers traveled around the region particularly in the lumberwoods and brought songs with them.

These recordings are available online at archive.org, but the index is unreliable and the recordings are hard to listen to. My partner Fred and I are in the process of transcribing as many of the Maine recordings as we can. We have published the first book in a series called "Bygon Ballads of Maine

There are many more to be done. This link includes the index
https://archive.org/details/helenhartnessflanders?sort=-week

You can also visit the archive at Middlebury College

In addition, there are collections made by Fanny Hardy Eckstorm and her colleagues Mary Smyth and Phillips Barry from between 1920-1939. They published Minstrelsy of Maine, British Ballads from Maine and the Maine Woods Songster.   Flanders consulted with them and collaborated with Eckstorm on a newspaper column seeking old songs.

Eloise Linscott (Folksongs of Old new England) recorded throughout the region as well though she was warned out of Vermont by Flanders.

Horace Beck also did a fair amount of collecting here

I'm happy to help you navigate this stuff- julia@castlebay.net

Another helpful person is Brian Miller at Evergreen Trad who makes the links between the woods traditions of the Northeast and the upper mid-west