Depends on your viewpoint. If you see folksongs as little more than the popular music of any given era which have been allowed to grow old through the graceful process of being passed on from generation to generation - those written with the piano in mind will be along shortly.
If you're impatient, or rather more arty, there's any number of settings by the "collectors" - Vaughan Williams, Gustav Holst, Philip Heseltine.
And to state the blindingly obvious, a piano isn't all that portable, which would tend to detract from that much vaunted spontaneity which we're all supposed to burst out with...
Rather more to the point, there are precious few pianists who have the art of accompaniment at the centre of their playing to a degree necessary successfully to accompany folksong. If you can, get out and do it - the music (to quote Dave Swarbrick)doesn't mind.
KYBTTS