I am going to talk to these people tomorrow about buying a cylinder. It is my understanding that I need to get one with a riser tube, is this correct ? Am I on the right track going with a beverage grade CO2 ?
Yes, you need to get a tank with a riser tube. I would stay away from the beverage CO2. Find a good fire extinguisher refill shop. They also may have the ability to hydro test your cylinder.
Try a fire extinguisher supply/refill shop. They are by far the cheapest I've found and have a bounty of used tanks they need to dispose of. Many will give you the tank if you pay for the pressure test and fill.