Recertifying nitrous bottles?

Welcome to rural Missouri :rolleyes:
When I get another bottle of argon/CO2 at the same store, I just put the empty one on the loading dock and they trade me for a full one (that is current stamped). They just can't handle a situation outside of their routine, apparently.
Here in rural VA I have the same problem. We had an old tractor farmers store that used to fill tanks they had just about everything helium, co2, nos, argon, oxygen etc but they went out of business and now there is nothing. We have a local welding store but they send everything off I and seriously doubt they do Nos!