Asafoetida Powder - Gluten Free
Frontier Brand is supposedly the only gluten free asafoetida readily available(rice rather than wheat flour mix) and their locator map says their stuff is sold at Whole Foods in Cupertino. Check your zip there may be one closer to you.
You should be able to find asafoetida at any Indian shop that sells spices, though I don't know about gluten free. I've gotten it at Milan on University Ave. in Berkeley, but I found it pretty vile smelling stuff and left it out the next time I made the recipe that called for it.