Clippard sells a variety of tanks besides the plastic ones. Even the smaller metal tanks will be heavier than the plastic ones, so keep an eye on how much weight you are adding if that is a concern.
http://www.clippard.com/products/cylinder-volume-tanks
All those tanks will take a long time to fill, so precharging the system before a match will be important. If you don't need quite as much force from some of your actuators, you can conserve air by reducing the pressure setting on your main regulator or by adding a second regulator set at a lower pressure downstream of the main regulator. This reduces the load on the compressor and may mean you need less storage.
If the regulator(s) cannot pass air quickly enough for some of your actuators, adding a small tank after the regulator(s) provides a reserve of working pressure air that can be delivered very quickly.