Yeah, it’s bizarre. I’ve been unsuccessful in finding .30-30. That is a round normally used in “cowboy style” lever-action rifles, not anything that would be banned. But on the other hand, it’s not a very popular round (and is 118 years old), and I’d think the .223 people would just buy .308 or something. For whatever reason, there is tons of 7mm-08, whatever that is, in my local stores.
Not really a WAG so much as a data point, but: .40 S&W is popular among cops, I believe. Maybe there was a surplus initially?