Tyler Patner , Avenge X project manager and also works for Pyramid Air responded. His explanation made sense to me why we don't have that bottle in the USA. His explanation is in the original thread. Here's an excerpt of his response:
1) What may not be clear to everyone is that the 400cc aluminum bottle used in many other parts of the world on the Avenge-X only fills to 250 BAR. Because of this, when you compare the 250 BAR fill bottle to the 300 BAR fill 210cc air tube, you only see a 5-10% shot count increase if you're comparing the same tune. Not a worthwhile increase in my opinion. Compare that with the 300 BAR bottle offered here in the US, and you get a much better ~40% higher shot count over the tube.
2) There are not very many 300 BAR bottle options in the diameter that it used on the Avenge-X (in fact, I am only aware of 2 others). Because of the modular design, and the fact that the drop block on the rifle accommodates both the tube and bottle without additional parts or modification, going to a larger diameter bottle was not in the cards.
3) They call it out in the video, but the rifle with the 250 BAR alu. bottle fills via a fill probe. You will notice a QD on the neck of the bottle, but the position of that QD is not easily controlled (meaning it doesn't always end up where you want it and can access it) and on some models of the rifle, it would be covered by the stock itself. I know fill probes annoy (that may be putting it mildly) most of us, and that was a concession we were not willing to make with the Avenge-X for the US market.