I have a very small midwest grocery store, and even they carry them (although they're cheaper if I go to Dubuque to the Asian market). The most "American" brand I've found (i.e., one you're likely to find in an Asian dept of your grocery store, and will have instructions in English) is "China Bowl" brand and come in a bright orange wrapper. They make both bean threads and rice noodles, and I'm not sure which your recipe calls for, but I'd go with the rest and use the mung bean. In Hawaii this dish is often called "Chicken Long Rice". Can I come? Anyway, just follow the package instructions.
Oh, p.s.; be careful. With both types of noodles, there's a short distance from Great Noodles to mush if you overcook. In serving, it also helps if after you prepare them, you take a pair of scizzors and cut the drained noodles through many times to shorten them. Makes them easier to serve with a spoon (otherwise sometimes you wind up picking up half the bowl of noodles every time you try to put it on your plate).