Sometimes they'll tell you and sometimes they won't. But, it never hurts to ask.
Once I had an "Iranian" restaurant bring me OUT some tea that I really fell in love with. They told me that I could not buy it there in the area but that they wanted to GIVE me some since I was such a loyal consumer of their Thai food. I ate there about once per week for a number of months.
Another thing you might want to do is start asking around to everyone you know - and looking in the yellow pages too - for Asian Groceries. There are many chinese, indian, thai, and even Filipina groceries that have new products you've never seen. Often times the packages are written in the native language - but, you could try asking the people that work there because they can likely translate for you.
In Tampa, Florida I remember there was a big grocery called, "Oceanic" and it's where EVERYONE went to shop for the food they served at their Asian restaurant. Whether it was Thai, Japanese, Chinese, or whatever. They had a great selection of fresh fish too.
So - check out your Asian markets! Ask your waitresses and cooks - where do they buy ingredients from? What is the name of a certain vegetable. My favorite vegetable here in Thailand is "Pak Boong". In America it's called "morning glory". I wonder if you can find it there. I've not looked since when I lived in America I never knew of the vegetable. I'm sure we have it! Let me know if you find it and try it - or, order it at the next Thai restaurant you visit!
:P