Quite a lot missing from that list, but I assume you have some of it and just haven't listed it?

From the pneumatic side of things:

Some sort of solenoid valve and a way to fire it, the ways i've used is a switch pressing a servo or a Battleswitch.
Ram
piping, connectors, etc...
on/off valve for the CO2 tank
buffer tank (optional)

Possibly more but I can't think off the top of my head.