A few weeks ago, I stumbled upon what seemed to be a new Vietnamese-oriented supermarket in Chinatown - Tan Tin Hung Supermarket at 121 Bowery Street. (That's what it says on the bag anyways.)
The name doesn't sound Vietnamese but they have tons of Vietnamese and Thai ingredients.
Here are some of my finds:
1) Cha Lua - A few different brands plus the fried kinds.
2) Cha Ca - Again, a few different kinds
3) Vietnamese Herbs - Ngo Gai, Basil, Dap Ca
4) Duck Balut and Chicken Balut
5) Banana and Pandan Leaves
6) Tons of different kinds of frozen Vietnamese Products
7) Lemongrass - Whole Fresh and packaged, processed
In the back, they also have a selection of frozen Vegetarian mock meats.
(I'm not affiliated with this store - just a Viet-American on the search for Vietnamese groceries in the City.)