Ukraine, and by extension most of the world, probably needs much more AA guns than there are in active duty right now. Before the advent of drones and loitering munitions those got increasingly mothballed and/or scrapped or just kept in deep reserve for use against helicopters. Now they're as useful, if not more, than they were in WW2.
Problem is that there simply aren't many AA guns around anymore. There's the Bofors 40mm/L70 that is still in production and getting upgrades, but apart from that one most are old designs. There's the Swiss Oerlikon GDF 35mm AA guns, but since it's Swiss it's possibly not allowed to be used in a war (though the Gepard uses those guns), but since Oerlikon is now owned by Rheinmetall that restriction might not exist anymore.
Other than those two most AA guns are actually ship-mounted turrets with some autocannons, generally Gatling-based and of lower caliber (20-30mm). Some big AA guns still exist, but those are all legacy systems.
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