User blog comment:TheRedScorpion/28/07/11 - Red Scorpion's Painting Table/@comment-9734625-20110808213939/@comment-4206721-20110812001737

The assault cannons are spare "bitz" but you can order the sprues from the GW website. They double the cost of the razorbacks pointswise. It does however allow your razorbacks to prang tanks and rend infantry.