I've used a couple...they were great motors. But as GL-P sez, they are currently OOP. Even when in productions they were special runs. RocketVision's G55s were also made by AT.
Yeah, a couple weeks ago I sacrificed a MachBuster on a G55. About 1200 feet it was outta sight. No one saw where it went, where it came down, but it was a gas watching it squirt off the pad. I've got one more MachBuster unbuilt and one more G55......just another sacrifice.