You would need to get hold of an Armageddon tank valve (if you don't get one with the reg), since geddy tanks are removable from the reg, with the pin valve loctited into the tank. If that doesn't make any sense, go to AA's website and download the manual and hopefully that will make things clearer
As far as I remember, the tank threads on the valve are standard (.625-18?), so any standard tank should fit it.