The mushrooms can be bought dried in asian supermarkets, both as whole and as shredded.
As they are purchased dried they need to be soaked in water for a few hours, either overnight before being used or soak them in boiled water for approx. 10 - 20 min.
The mushrooms has doesn't have a lot of flavour but it adds consistency and is good for wok dishes as well as a part of the filling of spring rolls.
I tried to buy and find images of white wood ear mushrooms but they don't seem to be a very common product. Images of the white mushrooms can be found when searching after the Vietnamse name: "nấm mèo trắng" (trắng = white).
