I'm about to do an in-take appointment to get into therapy myself, and I'm hoping to focus on handling my mood disorder, rather than my (healthy and functional) relationship status.
The term I'll be using as a starting prompt is "sex-positive". A counselor or therapist who professes to be sex-positive seems likely to be more open to poly clients.
There's also some informational pages designed for professionals interacting with us, once you've broached the topic, so that you don't have to go over vocabulary and ethics:
This article is just good in general as intro, though not professional-specific, fairly recent:
Good luck to us all!