We met a poly-friendly counsellor by getting a referral from a friend in the BDSM scene for someone who was BDSM-friendly.
I wouldn't say it's automatic, but I'm guessing that a lot of BDSM-friendly counsellors would also tend to be more open-minded to alternative lifestyles in general, which includes poly. BDSM communities tend to be a lot "bigger" than poly communities, so it can be easier to find people to get referrals for a good counsellor who's alternative-lifestyle-friendly. Maybe check FetLife to find people in your local BDSM scene.
Another option, look for your city's alternative-living/new-age magazine. They're usually on the rack in front of small/local/independent health food stores (i.e. not GNC) or alternative bookstores. They usually have ad sections for alternative medicine practitioners to advertise their services. That's how we found a good alternative-friendly counsellor after moving to a new city.
Gralson: my husband (works out of town).
Auto: my girlfriend (lives with her husband Zoffee).
The most dangerous phrase in the English language is "we've always done it this way."