Times have changed and in this case not for the better. I wish I had some great suggestions or secret sauce to recommend to you, but as joe notes in his post there are no reliable sites to find a ProDomme.

The best I can hope for is to do a simple google search in a given city for "Dominatrix" and then look at the search results. I look for professional websites and other social media presence that demonstrate some experience and some expertise. Once I have a name I then search that specific Domme looking for any kinds of reviews or social media trail. I even search the review forum here and on MF to see if there is anything useful posted.

Assuming no red flags pop up, I reach out to her to request a session and to discuss the details, being careful to follow her protocols. If those conversations go well I go ahead and schedule the session. It is a lot of work and far from foolproof, but it's the best plan I've been able to come up with to compensate for the lack of reliable places to look for Domme advertisements.

I know it doesn't answer your question and sorry I couldn't be more help, but this is what we subs are reduced to!
Jack