Like Katie already asked, are you being followed by a metabolic clinic? If you aren't you might want to try contacting one. Your best bet might be contacting the clinic that you were followed at as a child. They might be able to point you in the direction of programs that can help you or they might be able to provide you with a few samples until this can get figured out.
I personally have not experience this issue, and hopefully it will be awhile before I have to fight with an insurance company haha! I am still under my parents insurance, and the state I am in provides my formula for me. However, it drives me insane when I hear stories of how difficult it is for others to get their formulas and foods. I wish you the best of luck, and as always let us know if there is anything we can do to help.