Thanks to Mr. Wizard for finding and posting this useful information.
Naturopath docs are often certified as "Functional Medicine" docs too. You can locate both here:
Naturopaths by state: https://naturopathic.org/search/custom.asp?id=5613
Functional Medicine docs by state: https://www.ifm.org/find-a-practitioner/
From ANH: https://integrativepractitionersearch.com/ (a third search tool, thanks to Grulla)