It's Ramblin' Jack Elliott's "912 Greens". It appears on several of his records, including "Legends of Folk" on Red House, "Young Brigham" or Reprise (reissued later as "Me & Bobby McGee" on Rounder), and "Kerouac's Last Dream" on Folk Freak (reissued on Appleseed).

I believe the Rounder and Appleseed titles are in print on CD.