http://cgi.ebay.com/CO2-regulator-solenoid-magetic-valve-control-/250621512666?pt=LH_DefaultDomain_0&hash=item3a5a34cbda - That's all I got.
Up here it costs about $50-60 to certify and attach the correct nozzle onto a CO2 fire extinguisher or other suitable CO2 bottle.
They had brand new 5kg Cylinders for sale @$295 each. The company's name is National Gas; so maybe you have a branch relatively local to you.
It costs $7/kg for CO2 when you refill a cylinder, so the Fluval CO2 devices are not worth it in my opinion.
The $200 you are going to spend on the Fluval kit can be spent on a smaller CO2 fire-extinguisher. Once it's certed, it'll be cheaper to run and will cost you less.
The only thing that will cost more is the regulator + solenoid (linked above). That's about NZD $100 over what ever else you spend.