I've been wondering myself!

I use BackPage, and do OK, and am on ErosGuide, as well as having banners on numerous BDSM and Spanking sites. I am fairly low volume, and plan to keep it that way, but a couple more kinky playmates are always welcome

Quite a few advertise on Eros Guide.  They have a BDSM and Fetish section.  In fact, I see Madame Patricia's ad there now!