A lot of US sellers use the A-AAA. I am noticing it a lot more lately as well. Nearly all dealers I have met in Hong Kong use A-AAA now. Even some producers in Tahiti use A-AAA.
I took this picture at the "Service De La Perliculture" in Papeete. There was a huge lot getting prepped for auction and all of the bags were graded A-AAA.
Here is a breakdown.
http://www.pearlparadise.com/Tahitian-pearl-grading.htm