General Order 30 is most definitly in the OR Series 2, Volume XXII, part 2, pages 237-44. It was issued April 22, 1863, from Major-General Samuel Curtis. He also included a definition of a spy, correspondence with the enemy, the Partisan, the Brigand, and disloyal persons.
According to Richard S. Brownlee in his "Gray Ghosts of the Confederacy," General Curtis issued it "for the record" but "advised his subordinates that the guerrillas 'deserved no quarters; no terms of civilized warfare. Pursue, strike, and destroy the reptiles...'"
Rose Mary Lankford