I almost hate to say this but if you are a good customer at one of the popular tube stores, you will have no problem buying tubes.
Tube shortage?
One of the major suppliers of amplifier tubes is Russia. In retaliation to the sanctions levied against them, they decided to cease exporting tubes to the US and NATO. China makes tubes but your favorite tubes might come from Russia. The US makes almost no tubes. The Kremlin announced the suspension of exports would last at least through the rest of the year. If you have tube amps, you might stock up.