From what I've experienced - American, United, US Airways (my standard 3 pn free airlines) all have warmed tree nuts in first class (I usually don't smell it if I sit on the wing or farther back) and all have a buy-on-board option which includes a pack of tree nuts.
I think calling each and asking for the disability coordinator specifically and find out which can give you a buffer zone will be the strategy. Then, of course, talk to the flight attendants on the day to make 500% sure they won't walk through the coach cabin with warmed tree nuts as their own snack in the back of the plane. That happened once, and 30 minutes after I went back, made them get the head flight attendant, and chewed them out nicely. Just so happened they weren't supposed to do that anyway and broke the rules.
Good luck! Other options to consider, not sure how far you are from where you are going in AZ -- is train or driving?
Adrienne