Jon, if you're going out to play check with the event/organiser/field as far as I could see the use of bottles was free at WC, even Stakos (which I think have never been approved for use in the US) but as Tim says, DOT is the standard for the USA.
Some cylinders were dual tested, but I'm not aware that there are new ones about, I could be wrong.
im 100% sure you are MEANT to have a dot test bottle however when I played NPPL most of our team just stole the bands from an official and put them on our air systems. Never got checked all day.
Pure energy do a Tri-Test bottle that is good the world over. Planet eclipse and Slothball have them in stock.
I have a spare DXS bottle which is DOT tested and still got plenty of test left if your looking to buy one. If you want more info just give me a shout.