Have you thought about computational/mathematical biology and neuroscience? Mathematical neuroscience is a really cool field that uses a variety of ideas from math and physics, including spin operators, information theory, dynamical systems and chaos, statistics etc... It might be up your alley.
It sounds like a large applied math department like University of Maryland, Texas, Minnesota would be your best bet. Those programs will have a a lot of different research areas available to you and you can see what you like. Also, keep in mind that switching grad departments is not something unheard and probably happens quite frequently.
BTW, a PhD is a lot of work for something you are not passionate about. You must have some passion in life about something, no matter how obscure or crazy it seems. What is it? You may be able to turn it into a science problem