Hi and welcome!
I'm in the US, too, with no local jade sellers so I buy online. I have purchased from sellers in Hong Kong with no issue and so far no import tax. You might incur import tax if your purchase is expensive & your seller labels the package accurately. You cannot buy directly from Burma, but would have to go through other sellers. If you can see my signature, I have listed + linked the jade threads we have, including the seller thread and the a semi-precious stone thread.
As for testing the quality of the jade.... Do you mean for translucency, color, grain, inclusions, or do you mean to check if it is untreated? To check if jade is untreated, I have a UV light that shines on both short wave and long wave to check if the jade fluoresces, and I will use a kitchen scale to check the specific gravity. I have a loupe to look for spider-webbing, and indications of color polish. For bangles, I listen for a high clear chime.
However, untreated Grade A jadeite doesn't always equal expensive or "good quality". Even untreated jadeite can be opaque, full of inclusions, cracks, and stone lines, large grains, and uneven coloring. It's sometimes a hunt to find a balance between quality and price, but there are treasures at all price points! Jade is a true addiction.