The only product of this type that I’ve seen, so thought I’d email it around.
Concrete troughs that stack to whatever height you need, each ‘ring’ interlocks/seals and sits on a base so that can be filled with soil (not just a shell for placing pots within).
Comes in rectangular or square. Presents really well.
Manufactured in Australia, based in Sydney, but ships around Australia. (freight cost depends on order)