Yep ,it is a 12-stringer. I have "Where Have all the flowers gone " as well,but yes,no luck here.
But a somewhat strange idea passed my mind ,some of the chords seem definetly similar to those of "Bells of Rhymney" to me, with its subtle variation on the same chords (D,Dsus4,A,Asus4).
Could that be? Still no idea on that bass line tho.