If you go to the homemade cracker thread, I posted a few wheat-free/vegan cracker recipes. They are not really hard enough for teething though.
I have a couple of teething cracker recipes in my book Simply Natural Baby Food.
One is Zwieback which is made from bread. If you have get wheat free bread like rice, spelt, rye etc. you could make this as follows:
Preheat oven to 250. Cut slices of bread into strips about 1 1/2 inches wide. Plae on baking sheet. Bake one hour, or until strips are dried out and hard.
My other teething cracker is wheat free but I couldn't get it to keep that hard texture without using egg yolk. Let me know if you want me to post it anyway.