Well that makes it easy.
I believe part of the NFPA spec is that they are repairable, so you might look into a kit for the old
cylinder to keep on standby. Two is one and one is none.
BUT!
How did the cylinder get condemned in the first place? We have ROQ/MHM machines, but have never had
a cylinder go bad. We have had plenty of valves go bad though which can look similar.