Penrith has a great range of shops for its size. Although I can't think of a specific shop, I can pretty much guarantee that someone in town will have the right cylinders. If your first shop has the wrong cylinders, they'll probably still be able to point you straight to someone who has the right sort. All the shops are easily reached from the railway station. You can either come back to the railway station to catch the Threlkeld bus, or catch it at the bus station, which you'll find tucked away behind the Co-op.
