Both the aforementioned esoterica web portals and many specialized websites devoted to various seminars will usually publish seminar-enrollment announcements – sometimes for free and sometimes for a fee. The total number of such sites may number in the dozens. Even free announcements can garner a good response when published.
It makes sense to publish free announcements wherever you can. You might do so on websites devoted to these kinds of phenomena. There are also paid services that will automatically publish your announcements on thousands of such platforms. You can’t expect a massive response overnight, but such services might benefit both your event and the website that the links in your announcement point to.