I believe that if you are outside of a certain radius you can use civilian providers. First you need to talk to tricare to find out if you are outside of the area, they can also tell you providers that accept tricare near you.
I actually was just doing something similar today since we just PCS'd to Texas. I'm guessing you are in tricare south which is run by Humana Military. The phone number is 1-800-444-5445.
You can also look up a lot of this info online at www.humana-military.com. You can print out the health insurance cards there if you need a temporary one. I'm taking my daughter to an appointment today and printed one out with her new info.