They cannot be shipped to locations which grow commercial cavendish for risks of viral infection. Australia has restrictions in place on movement of all kinds of fruit and vegetables inter-state for exactly this reason.
Also, if travelling in S.E.Asia try the small "sugar bananas" and ladyfinger, commonly available in a few places alongside some of the dozens and dozens of "not-cavendish" bananas that locals eat.
I've seen a few places sell them. It's a specialty item and I suspect you need a specialty grocer or be some place where you can grow them. (e.g. in the tropics or semi-tropical spots, you can grow a variety of banana varieties that you can't really find in stores).