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I did some searching and found this site with GF spices including
asafoetida. They state they use rice flour.
http://www.natco-online.com/acatalog/spicesection.html
Here is a quote from their website:
"NATCO SPICES FOR INDIAN COOKING

GLUTEN FREE SPICES
Natco spices are made without compromise. Certain spices like
Asafoetida are a resin in the natural state and need to be combined
with a flour base for culinary use. Our competitors often use wheat
flour, but Natco uses only rice flour which ensures our spices can be
used by those with gluten intolerances such as coeliac sprue and does
not impair the purity of the flavour.

Our ground spices do not contain any wheat flour as an ingredient."

Barb (gf since 1981)

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