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What an incredible number of responses to my question of what to use to make gravy!!!
My thanks to all.  

A 2/3 majority use corn starch.  Others use sweet rice flour, sometimes in combination with other flours and sometimes alone. 
And some use their regular GF flour mix.  A few use arrowroot starch and/or potato starch.

I will copy the most interesting response below in case someone wants to try this method.  

One of the members in our group tipped me to to toasted sweet rice flour years ago.  It works pretty much like wheat flour & the longer you cook it, the thicker it gets.  ...In essense, you are making your own 'modified' food starch! 
 
Heat sweet rice flour (check Mochinko brand at grocer's oriental section or by the bag at oriental grocery) in a dry pan over medium heat, stirring constantly, until it smells goodIt ca be mixed with water or even just sprinkled into pan dripping & it will cook up without lumps pretty much, like wheat flour did/does.
 
Be careful since hot flour is slipperier than hot oil--I actually had to vacuum my stove the first time I tried it! 
 
You will probably want to cool flour on a cookie sheet to stop it from burning since pan will stay hot after heat if turnned out.  
 
I usually do half a cup or more in a large skillet & keep it in a jar until later. If toasted darker, it can be used to thicken sauces to give effect/flavor similar to roux.  It ends up being more of a gravy technique but it creates the same effect/flavor since the whole browning flour in oil thing of roux doesn't really work when the flour isn't wheat.
 
Bev in Milwaukee  
 
I feel ready for Thanksgiving now thanks to all of you. 
 
Wishing you all a happy and delicious Thanksgiving.

Sarah
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