Peter, I can't help you with programs that are completely trad music.

I can tell you that WUMD (UMass-North Dartmouth) has some folk programming that includes some trad music. I often listen to Celtic Stew on Saturdays from noon to 3. You can see the schedule here. http://www.893wumd.org/programs.html

WRIU (University of RI) has some folk music most evenings from 6-9. I often listen to Kingston Coffeehouse and The Celtic Realm. Their schedule is here. When you click on the link, the page will appear to be almost blank, but if you scroll down you'll see the grid. http://www.wriu.org/programming.htmlI see that the Monday program is now called Traditions, That's a change from the previous title and I haven't listened to it. That slot used to have a lot of Cajun, Zydeco, and bluegrass music. I'll have to check it out next week, because it ended about 15 minutes ago!