A 20FT High Cube costs a carrier the same vessel slot as a 20FT Standard while carrying only about four cubic metres more, and it is produced in small runs because demand for it is small. The result is that carriers rarely order or reposition them, so they almost never reach depot surplus and are normally built to order.
Container plants schedule around the 40HC, which was about 94% of August production plans across the network. Standard 20-footers take up most of what remains. The 20FT High Cube is a further exception inside an exception: a taller shell on a 20ft footprint, requiring its own panel sizes and its own line changeover for a run that is short.
Short runs price differently and schedule differently. That is most of why a 20HC quotation sits above a 20GP quotation by more than the extra steel would suggest.
A carrier sells slots. On deck and in the hold, a 20ft slot is a 20ft slot whether the box in it is 8'6" or 9'6" tall, and the taller unit complicates stowage planning against standard-height neighbours. The carrier gains roughly four cubic metres of capacity and takes on a planning constraint, which is a poor trade at fleet scale.
So carriers buy few of them, and the ones in circulation stay on the trades that specifically need the height rather than being repositioned around the world.
Depot surplus is a by-product of repositioning. Equipment accumulates where carriers move more boxes in than out, and it accumulates in the types they move in volume. A container type that is barely repositioned barely accumulates.
In practice, used 20HCs surface occasionally, at prices that reflect scarcity rather than condition, and often at cargo-worthy grade rather than anything close to one-trip. Waiting for one is a supply strategy with no supply behind it.
If you need the height on a 20ft footprint, plan a factory order and plan it against a production month. Lead time runs on the same roughly ten-week cycle as the rest of the network, and the units are delivered on a first trip because that is what makes moving a small batch across an ocean economic.
The full specification is on the 20FT High Cube page.