I live on the Eastern shore of Maryland and exotic ingredients are very hard to come by!
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It's just a brand of all purpose flour. Any all purpose will do.
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Wondra is an exceptionally fine flour. You can make any all-purpose flour into a Wondra-style flour by buzzing it for a few seconds in your food processor with the metal (chopping) blade.
Wondra Flour is actually not All Purpose Flour, because it is made of malted barely flour and wheat flour. It is a low-protein, instant, flour, meaning it has been partially cooked as to dissolve very fast when added to hot liquid. As for acquiring Wondra Flour, Amazon is your friend. http://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=wondra+flour&x=0&y=0
Mr_Vittles is right in the description of Wondra flour. I've even found Wondra flour at my local Wal-mart, so you might be surprised at how widely available it is (marketed as a gravy thickener, only $2 for 13 oz).