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Thanks to all.  The suggestions were these

(1) Get a stainless steel thermos, not plastic.

(2)  Try www.thermos.com

(3)  Target has them.  Try the camping good section (AHA! Silly me,
looking in the housewares and dishes section!)

(4)  Wal-Mart has them (I refuse to shop there because they sell handgun
ammunition, but that's a whole other issue!) :-)

Some people suggested I work with the school to arrange GF hot lunches for
her.  That might be a good idea in some place, but I've seen the hot
lunches at our school and all I can say is YUCK!  (Some of her teachers
have asked me if I would start packing lunches for them, too.)

Thanks again!