either
Doctors Data Lab or Genova (used to be Great Smokies Diagnostic Lab)
http://doctorsdata.com/tests_assessments_info.asp#Gastrointestinal
The less you do the cheaper. "Comprehensive Stool Analysis" or just for yeast "microbiology profile."

Genova has suggested tests for CF inparticular - it is interesting just to see what is availble if you ever have a nagging suspicion.
http://www.gdx.net/home/assessments/finddisease/cystic_fibrosis/

"comprehensive digestive stool analysis"

You could give a call and see which one has the better price for what you need...Each site has sample results so you can see how your results will be presented