Applesauce or mashed bananas, or a combination of both.

For an ingredient substitution chart, go to pcrm.org -- they have an extensive chart with egg substitutions. Eggs serve various purposes in baking, so you want a sub that will keep it from crumbling. I'd look for something along the lines of flour + water -- to paste the bars together...

I have heard about using ground flaxseed--look at gluten-free recipe sites maybe. I'm making marshmallows at the moment, or I'd look this up myself--I'm curious too!