Well, the old standy is:

http://thistleradio.com/

...which may or may not be on in your NPR market.

The MIdnight Special (WFMT, Chicago but also syndicated nationally mostly to classical music stations) does play some but not exclusively. MidSpec has gotten increasingly "folky"...years ago it was a great balance between folk, ethnic, comedy and show tunes.

Other than those and Greg's (Beloitpiper) and one broadcast by the University of Chicago FM station (which has, I think, about a five watt transmitter...range is maybe four city blocks), I can't think of any more.

Best

AA