4757 Melrose Ave.
LA, CA 90029
There are quite a few 99 Ranch stores... just drive east on the 10 past downtown and you'll hit one in Monterey Park/Alhambra. It's farther than Bangkok Market though.
And you might try your original grocery stores again, but this time ask for it in its different names... glass noodles, rice vermacelli, bean thread, it all refers to the same thing.
Any market that carries Asian items. All different Asian cuisine use them. "Glass noodles" are made from mung beans and they may be sold as "bean thread noodles." I've even seen them in Ralphs markets which have Asian food sections.
You might even go into a Chinese or Asian restaurant and ask them to sell you a package--they're cheap(the bean thread noodles that is).