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I've tried many substitutes for bread crumbs (cooked rice, baby rice
cereal, puffed rice, etc) but I recently stumbled into the best one I've
found yet, while cooking at my daughter's house and trying to figure out
what I could use in her non-GF kitchen.  I had brought some Lundberg's
brown rice cakes with me, so I stuck them in the blender on the "crumb"
cycle...and they came out great. They had the right dryness, size,
consistency... like real bread crumbs! I used them in my meatballs, and
they were a big success. (Before grinding them, I broke them up into
large-sized pieces.) Judy Beck/Santa Cruz, CA.