Yeah, generally speaking every town has at least one place that supplies all gases, co2, butane, argon etc. Some are more specific to welding and some for caravans etc but there's at least one in every town around me. FE on the other hand, the nearest place to me is about 30miles away so its actually easier for me to get pub bottles than my FE changed. Now that I've had mine changed a few times I have the mobile number of the various guys who service fire extinguishers in my area. When I'm due one I just give them a bell and meet him the next time he's in town. They tend to serve business's changing Fe's when they are due a check, usually they will just give them a new FE and take the old one away to be checked, re-date it and pass it on to the next customer rather than servicing it on site so they usually have a few in the van which they know are still in good working order.
Must be something to do with H&S that they replace them every 12 months or so.