In email, I usually just ask if they ever meet with fans and see how they respond.  There's no illegal question in there, and they can assume anything they want.  Sometimes I get a response like "I don't tour", or "I'll be at X" where "X" is the name of some convention or show or club.  Sometimes, I get a response that adds "If you mean private meetings then..." and she'll say whether or not she does.  Sometimes she'll respond with a question like "what do you mean?"  If the response I get back leaves open the question, I'll send another email.  Sometimes it takes a few rounds and in the meantime, I chat with her like I would meeting any woman in any location that I was interested in, and let her get to know me a little and make sure she knows I'm not LE, a stalker or anything like that.

I think all the women who do porn these days know that some porn stars escort and a guy asking a porn star if she meets with fans is really asking if she escorts.  I think the girls know this and will respond accordingly as long as you're polite and cool about it once they know you're not LE.

I've had some success with this approach and I've had some success with similar approaches at conventions although there are other methods that can be used in person.  

When it fails, I just ask someone "in the know" - someone I already have a connection with who can vouch for me.