Niles recorded a couple of 10" LP's on his own BOONE-TOLLIVER label
around 1953. BTR-22 American Folk Love Songs.
             BTR-23 Ballads Vol.1
They are not common, though are offered from time to time on the various sites for vinyl.

They are now available on a CD with notes by RON PEN, director of the John Jacob Niles Center for American Music, University of Kentucky.
I'm Goin' Away
The Lass from the Low Country
Go 'way from my Window
The Cuckoo
Barbary Ellen
Little Mattie Groves
The Turtle Dove
Black is the color of My True Love's Hair
Mary Hamilton
The Little Mohee
The Rosy Peach
The Gypsy Laddie
O Waly, Waly.

Available from your favourite purveyor of little silver discs.
Best wishes, Thomas.