What do you consider folk music? I generally consider it anything that I can play in my living room on recorder(flute), guitar, mandolin and harp that wouldn't annoy my mother and I could probably play in church. Unplugged, as it were.

Where do you live? Do you have access to National Public Radio and if so does the local programming have a "folk show" feature? WPSU from State College, Pennsylvania has the Folk Show on Fridays, Saturdays and Sundays (check out the live streaming music). We also get The Thistle and Shamrock on Sunday afternoons and The Prairie Home Companion on Saturdays. These are two programs with lots of folksy music.

If you live on the East coast, go to the Old Songs Festival in Guilderland NY or the Philadelphia Folk Festival. I've been to Old Songs and you'd learn a lot.

Folk songs and music are "the peoples music". In the old days itinerate harpers would pass on tunes they learned while learning new songs when they went from town to town. A many songs were "local" in style and not even heard the next valley or two over. The artists you mention were our nation's folk musicians and there are many more for you to discover. And yes, church is a good place to get more music! Check out the Oxford Book of Carols and then check out the group Nowell Sing We Clear. Everything they sing is from that book. We use it in church during Advent, Christmas and the Easter seasons. The new addition to our hymnal as a tune by Dylan and songs about segregation and Martin Luther King jr in it.

Enjoy your search! Dig away merrily. And google a lot.