A collector named Tom has posted on the Hobby Bunker forum that Barzso has done Union siege artillery.
Update 9/20/13
Jim Clouse has posted photos of the new Barzso Collectibles Union siege artillery on the Hobby Bunker Forum. I am sure you will see them on other sites. Jim has also posted prices for the various items that make up the union siege artillery. I have listed them below The figures are in resin.
Artillery Crew (blue or gray) – 6 figures for $14.95
Semaphore Man – (includes 2 figures, 1 each of blue and gray w/2 poles and flags) – $7.98
Parrott Gun (1 cannon w/small foam base) – $14.95
Armstrong Gun (1 cannon w/small foam base) – $14.95
Rodman Gun (1 cannon w/small foam base) – $14.95
Columbiad (1 cannon w/small foam base) – $14.95
Late era Civil War Fort (sold piece part):
One straight section (~20″ long) – $50
One gate section (~20″ long) – $50
One Corner section – $40
Signal tower – $13